Vice-Coordenador
IF-USP
Gustavo M. Dalpian
Publicações
2026
Braz, Lauro B.; Rivera, Daniel D.; Lopes, Emmanuel V. C.; Martins, George B.; Dalpian, Gustavo M.; Silva, Luis G. G. V. Dias
Ni-O hybridization as a stabilizer for $s^±$ superconductivity in La$_3$Ni$_2$O$_7$: a DFT+RPA study Miscellaneous
2026.
@misc{braz2026niohybridizationstabilizerspmc,
title = {Ni-O hybridization as a stabilizer for $s^±$ superconductivity in La$_3$Ni$_2$O$_7$: a DFT+RPA study},
author = {Lauro B. Braz and Daniel D. Rivera and Emmanuel V. C. Lopes and George B. Martins and Gustavo M. Dalpian and Luis G. G. V. Dias Silva},
url = {https://arxiv.org/abs/2609.05185},
year = {2026},
date = {2026-09-04},
urldate = {2026-01-01},
abstract = {The superconducting gap symmetry of high-pressure bilayer nickelates remains under debate, with weak- and strong-coupling approaches yielding different pairing tendencies. In this work, we investigate how the weak-coupling treatment of electronic states away from the Fermi level influences magnetic fluctuations and superconductivity in La3Ni2O7. We employ a full-spectrum model based on orthonormalized projections of Kohn-Sham states onto local Ni-eg orbitals, which preserves the density-functional band structure while redistributing spectral weight over a wide energy range. Compared to a low-energy description, this approach yields enhanced interlayer spin fluctuations and a commensurate magnetic instability. Within a spin-fluctuation framework, these features favor a sign-changing s± superconducting state, whereas low-energy models tend to stabilize d-wave pairing. Our results suggest that interlayer coupling in full-energy models may play an important role in shaping the predicted pairing symmetry of bilayer nickelates.},
keywords = {},
pubstate = {published},
tppubtype = {misc}
}
The superconducting gap symmetry of high-pressure bilayer nickelates remains under debate, with weak- and strong-coupling approaches yielding different pairing tendencies. In this work, we investigate how the weak-coupling treatment of electronic states away from the Fermi level influences magnetic fluctuations and superconductivity in La3Ni2O7. We employ a full-spectrum model based on orthonormalized projections of Kohn-Sham states onto local Ni-eg orbitals, which preserves the density-functional band structure while redistributing spectral weight over a wide energy range. Compared to a low-energy description, this approach yields enhanced interlayer spin fluctuations and a commensurate magnetic instability. Within a spin-fluctuation framework, these features favor a sign-changing s± superconducting state, whereas low-energy models tend to stabilize d-wave pairing. Our results suggest that interlayer coupling in full-energy models may play an important role in shaping the predicted pairing symmetry of bilayer nickelates.
Vieira, Pedro Roberto Lopes; Rivera, Daniel D.; Farigliano, Lucas Martin; Sabino, Fernando P.; Dalpian, Gustavo Martini
Alloy engineering of Magnetic phases in two-dimensional Chromium Trihalides Journal Article
Em: arXiv e-prints, pp. arXiv:2607.10030, 2026.
@article{2026arXiv260710030L,
title = {Alloy engineering of Magnetic phases in two-dimensional Chromium Trihalides},
author = {Pedro Roberto Lopes Vieira and Daniel D. Rivera and Lucas Martin Farigliano and Fernando P. Sabino and Gustavo Martini Dalpian},
doi = {10.48550/arXiv.2607.10030},
year = {2026},
date = {2026-07-01},
urldate = {2026-07-01},
journal = {arXiv e-prints},
pages = {arXiv:2607.10030},
abstract = {Two-dimensional magnetic materials offer unique opportunities for exploring low-dimensional spin phenomena and next-generation spintronic devices. Chromium trihalides CrX3 (X = Cl, Br, I) belong to an important family of these materials, where alloying opens pathways for tailoring their electronic, magnetic, optical properties, and thermodynamic stability. In this work, we present a density functional theory study of CrX3 compounds and their ternary alloys. Our results show that for the pure compounds, the ground state is ferromagnetic (FM), with the antiferromagnetic-zigzag (AFM-Z) and paramagnetic (PM) phases being close in energy. For these pure systems, the band gap variation among different magnetic phases does not exceed 0.16 eV, and the average magnetic moments on Cr atoms increase from Cl to Br to I. For the alloys, the FM state remains the lowest-energy configuration, but the energy difference towards the AFM-Z phase decreases for compounds with lower iodine concentration. The calculated band gaps reveal a pronounced bowing along the compositional edge connecting CrCl3 and CrI3. The Curie temperatures show a smooth variation across compositions, consistent with the nearly linear behavior of the magnetic exchange parameters. Based on the calculated mixing enthalpy and configurational entropy, the approximate Gibbs free energy indicates that alloy formation becomes thermodynamically favorable at finite temperatures, which is important to overcome the intrinsic experimental instability of these compounds.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Two-dimensional magnetic materials offer unique opportunities for exploring low-dimensional spin phenomena and next-generation spintronic devices. Chromium trihalides CrX3 (X = Cl, Br, I) belong to an important family of these materials, where alloying opens pathways for tailoring their electronic, magnetic, optical properties, and thermodynamic stability. In this work, we present a density functional theory study of CrX3 compounds and their ternary alloys. Our results show that for the pure compounds, the ground state is ferromagnetic (FM), with the antiferromagnetic-zigzag (AFM-Z) and paramagnetic (PM) phases being close in energy. For these pure systems, the band gap variation among different magnetic phases does not exceed 0.16 eV, and the average magnetic moments on Cr atoms increase from Cl to Br to I. For the alloys, the FM state remains the lowest-energy configuration, but the energy difference towards the AFM-Z phase decreases for compounds with lower iodine concentration. The calculated band gaps reveal a pronounced bowing along the compositional edge connecting CrCl3 and CrI3. The Curie temperatures show a smooth variation across compositions, consistent with the nearly linear behavior of the magnetic exchange parameters. Based on the calculated mixing enthalpy and configurational entropy, the approximate Gibbs free energy indicates that alloy formation becomes thermodynamically favorable at finite temperatures, which is important to overcome the intrinsic experimental instability of these compounds.
Lemes, Maykon Alves; Sabino, Fernando Pereira; Dalpian, Gustavo Martini; Souza, Jose Antonio
Lanthanide-induced magnetic functionality and conductivity enhancement in MAPbI3 via water-assisted recrystallization Journal Article
Em: Appl. Phys. A, vol. 132, não 7, 2026, ISSN: 1432-0630.
@article{Lemes2026,
title = {Lanthanide-induced magnetic functionality and conductivity enhancement in MAPbI3 via water-assisted recrystallization},
author = {Maykon Alves Lemes and Fernando Pereira Sabino and Gustavo Martini Dalpian and Jose Antonio Souza},
doi = {10.1007/s00339-026-09812-8},
issn = {1432-0630},
year = {2026},
date = {2026-06-22},
journal = {Appl. Phys. A},
volume = {132},
number = {7},
publisher = {Springer Science and Business Media LLC},
abstract = {<jats:title>Abstract</jats:title>
<jats:p>
Lanthanide incorporation into hybrid halide perovskites offers a promising route to introduce magnetic functionality while tuning charge-transport behavior. Here, we report the incorporation of paramagnetic rare-earth ions (Gd
<jats:sup>3</jats:sup>
⁺, Tb
<jats:sup>3</jats:sup>
⁺, and Dy
<jats:sup>3</jats:sup>
⁺) into MAPbI₃ through a water-assisted dissociation-recrystallization strategy that enables trapping of 4f ions within the restored 3D perovskite-derived lattice. Powder X-ray diffraction confirms preservation of the tetragonal I4/mcm structure, while ICP-MS verifies the presence of lanthanides in the final materials. Magnetic susceptibility measurements reveal robust paramagnetic behavior governed by the 4f electronic configuration, with effective magnetic moments of μ
<jats:sub>eff</jats:sub> = 9.12 μ
<jats:sub>B</jats:sub>
for MAPbI₃:Tb and 20.22 μ
<jats:sub>B</jats:sub>
for MAPbI₃:Dy. Electrical measurements show a pronounced reduction in dark resistance, decreasing from approximately 7.7 × 10⁷ Ω for pristine MAPbI₃ to about 1.0 × 10
<jats:sup>4</jats:sup>
Ω for the most conductive Ln-doped sample, indicating a substantial enhancement of charge transport upon lanthanide incorporation. Under illumination, all samples exhibit reversible photoconductive behavior. Density functional theory calculations, performed using simplified substitutional models, provide exploratory electronic-structure scenarios: Gd-related unoccupied 4f states may lie within or near the conduction band, whereas Tb and Dy can introduce localized f-derived states within the bandgap, which may contribute to carrier trapping and modified recombination dynamics. Optical absorption measurements indicate subtle bandgap modulation without significant changes in the radiative band-to-band emission. These results demonstrate that water-assisted recrystallization is a viable strategy to introduce magnetic functionality into MAPbI₃ while substantially modifying its electrical response, and they identify lanthanide-doped MAPbI₃ as a promising multifunctional platform for future optoelectronic and spintronic studies.
</jats:p>
<jats:p>
<jats:bold>Graphical abstract</jats:bold>
</jats:p>
<jats:p>A significant conductivity enhancement is observed when rare-earth ions are incorporated into an iodine-based 3D perovskite matrix. The results also reveal the emergence of magnetic functionality associated with the inclusion of 4f paramagnetic ions. Although the photoluminescence spectra of the doped samples remain similar to that of pristine MAPbI₃, clear changes in optical absorption and electrical transport are observed.</jats:p>},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
<jats:title>Abstract</jats:title>
<jats:p>
Lanthanide incorporation into hybrid halide perovskites offers a promising route to introduce magnetic functionality while tuning charge-transport behavior. Here, we report the incorporation of paramagnetic rare-earth ions (Gd
<jats:sup>3</jats:sup>
⁺, Tb
<jats:sup>3</jats:sup>
⁺, and Dy
<jats:sup>3</jats:sup>
⁺) into MAPbI₃ through a water-assisted dissociation-recrystallization strategy that enables trapping of 4f ions within the restored 3D perovskite-derived lattice. Powder X-ray diffraction confirms preservation of the tetragonal I4/mcm structure, while ICP-MS verifies the presence of lanthanides in the final materials. Magnetic susceptibility measurements reveal robust paramagnetic behavior governed by the 4f electronic configuration, with effective magnetic moments of μ
<jats:sub>eff</jats:sub> = 9.12 μ
<jats:sub>B</jats:sub>
for MAPbI₃:Tb and 20.22 μ
<jats:sub>B</jats:sub>
for MAPbI₃:Dy. Electrical measurements show a pronounced reduction in dark resistance, decreasing from approximately 7.7 × 10⁷ Ω for pristine MAPbI₃ to about 1.0 × 10
<jats:sup>4</jats:sup>
Ω for the most conductive Ln-doped sample, indicating a substantial enhancement of charge transport upon lanthanide incorporation. Under illumination, all samples exhibit reversible photoconductive behavior. Density functional theory calculations, performed using simplified substitutional models, provide exploratory electronic-structure scenarios: Gd-related unoccupied 4f states may lie within or near the conduction band, whereas Tb and Dy can introduce localized f-derived states within the bandgap, which may contribute to carrier trapping and modified recombination dynamics. Optical absorption measurements indicate subtle bandgap modulation without significant changes in the radiative band-to-band emission. These results demonstrate that water-assisted recrystallization is a viable strategy to introduce magnetic functionality into MAPbI₃ while substantially modifying its electrical response, and they identify lanthanide-doped MAPbI₃ as a promising multifunctional platform for future optoelectronic and spintronic studies.
</jats:p>
<jats:p>
<jats:bold>Graphical abstract</jats:bold>
</jats:p>
<jats:p>A significant conductivity enhancement is observed when rare-earth ions are incorporated into an iodine-based 3D perovskite matrix. The results also reveal the emergence of magnetic functionality associated with the inclusion of 4f paramagnetic ions. Although the photoluminescence spectra of the doped samples remain similar to that of pristine MAPbI₃, clear changes in optical absorption and electrical transport are observed.</jats:p>
<jats:p>
Lanthanide incorporation into hybrid halide perovskites offers a promising route to introduce magnetic functionality while tuning charge-transport behavior. Here, we report the incorporation of paramagnetic rare-earth ions (Gd
<jats:sup>3</jats:sup>
⁺, Tb
<jats:sup>3</jats:sup>
⁺, and Dy
<jats:sup>3</jats:sup>
⁺) into MAPbI₃ through a water-assisted dissociation-recrystallization strategy that enables trapping of 4f ions within the restored 3D perovskite-derived lattice. Powder X-ray diffraction confirms preservation of the tetragonal I4/mcm structure, while ICP-MS verifies the presence of lanthanides in the final materials. Magnetic susceptibility measurements reveal robust paramagnetic behavior governed by the 4f electronic configuration, with effective magnetic moments of μ
<jats:sub>eff</jats:sub> = 9.12 μ
<jats:sub>B</jats:sub>
for MAPbI₃:Tb and 20.22 μ
<jats:sub>B</jats:sub>
for MAPbI₃:Dy. Electrical measurements show a pronounced reduction in dark resistance, decreasing from approximately 7.7 × 10⁷ Ω for pristine MAPbI₃ to about 1.0 × 10
<jats:sup>4</jats:sup>
Ω for the most conductive Ln-doped sample, indicating a substantial enhancement of charge transport upon lanthanide incorporation. Under illumination, all samples exhibit reversible photoconductive behavior. Density functional theory calculations, performed using simplified substitutional models, provide exploratory electronic-structure scenarios: Gd-related unoccupied 4f states may lie within or near the conduction band, whereas Tb and Dy can introduce localized f-derived states within the bandgap, which may contribute to carrier trapping and modified recombination dynamics. Optical absorption measurements indicate subtle bandgap modulation without significant changes in the radiative band-to-band emission. These results demonstrate that water-assisted recrystallization is a viable strategy to introduce magnetic functionality into MAPbI₃ while substantially modifying its electrical response, and they identify lanthanide-doped MAPbI₃ as a promising multifunctional platform for future optoelectronic and spintronic studies.
</jats:p>
<jats:p>
<jats:bold>Graphical abstract</jats:bold>
</jats:p>
<jats:p>A significant conductivity enhancement is observed when rare-earth ions are incorporated into an iodine-based 3D perovskite matrix. The results also reveal the emergence of magnetic functionality associated with the inclusion of 4f paramagnetic ions. Although the photoluminescence spectra of the doped samples remain similar to that of pristine MAPbI₃, clear changes in optical absorption and electrical transport are observed.</jats:p>
Franca, José R.; Santana, Lucas A. R.; Soares, Cássio C. S.; Acosta, Carlos Mera; Dalpian, Gustavo M.; Souza, Jose Antonio
Dimensionality‐Driven Emerging Phenomena in Hybrid Metal Halides Journal Article
Em: Small Structures, vol. 7, não 6, 2026, ISSN: 2688-4062.
@article{Franca2026,
title = {Dimensionality‐Driven Emerging Phenomena in Hybrid Metal Halides},
author = {José R. Franca and Lucas A. R. Santana and Cássio C. S. Soares and Carlos Mera Acosta and Gustavo M. Dalpian and Jose Antonio Souza},
doi = {10.1002/sstr.202600018},
issn = {2688-4062},
year = {2026},
date = {2026-06-08},
journal = {Small Structures},
volume = {7},
number = {6},
publisher = {Wiley},
abstract = {<jats:p>Hybrid metal halides are unique among semiconductors in that their inorganic octahedral networks can be rationally assembled in 3D, 2D, 1D, and 0D forms, enabling dimensionality to assist as a powerful control knob over structure, electronic properties, excitations, and stability. This perspective unifies these systems under a connectivity‐based framework and examines how reducing dimensionality reshapes quantum confinement, dielectric screening, structural anisotropy, exciton binding and interaction, lattice distortions, electron–phonon coupling, and spin–orbit interactions, giving rise to a set of emergent physical phenomena: self‐trapped excitons and polarons, Rashba–Dresselhaus spin splitting, photon recycling and energy funneling, and spin/polar ferroic orders. Together, these phenomena reveal how dimensionality serves not merely as a structural descriptor but as a design principle that governs collective excitations and couplings among charge, spin, and lattice degrees of freedom. We critically assess, challenge, and highlight the importance of understanding emergent behavior in transitioning from phenomenology to the rational design of next‐generation optoelectronic, spintronic, and quantum devices based on dimensionality‐engineered halide perovskites.</jats:p>},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
<jats:p>Hybrid metal halides are unique among semiconductors in that their inorganic octahedral networks can be rationally assembled in 3D, 2D, 1D, and 0D forms, enabling dimensionality to assist as a powerful control knob over structure, electronic properties, excitations, and stability. This perspective unifies these systems under a connectivity‐based framework and examines how reducing dimensionality reshapes quantum confinement, dielectric screening, structural anisotropy, exciton binding and interaction, lattice distortions, electron–phonon coupling, and spin–orbit interactions, giving rise to a set of emergent physical phenomena: self‐trapped excitons and polarons, Rashba–Dresselhaus spin splitting, photon recycling and energy funneling, and spin/polar ferroic orders. Together, these phenomena reveal how dimensionality serves not merely as a structural descriptor but as a design principle that governs collective excitations and couplings among charge, spin, and lattice degrees of freedom. We critically assess, challenge, and highlight the importance of understanding emergent behavior in transitioning from phenomenology to the rational design of next‐generation optoelectronic, spintronic, and quantum devices based on dimensionality‐engineered halide perovskites.</jats:p>
Rivera, Daniel D.; Dalpian, Gustavo M.; Perdew, John P.
Identifying strong correlation using only the Kohn-Sham density of one-electron states Miscellaneous
2026.
@misc{rivera2026identifyingstrongcorrelationusing,
title = {Identifying strong correlation using only the Kohn-Sham density of one-electron states},
author = {Daniel D. Rivera and Gustavo M. Dalpian and John P. Perdew},
url = {https://arxiv.org/abs/2604.25125},
year = {2026},
date = {2026-04-28},
urldate = {2026-01-01},
abstract = {Strongly correlated systems have long been a central and highly non-trivial topic in condensed matter physics. At the non-interacting level, strong correlation can be associated with powerful (near) degeneracies between occupied and unoccupied states, which leads to a high density of states near the Fermi level in metallic configurations. Such regimes are commonly treated with beyond-density functional theory (DFT) approaches, such as DFT+U or DFT+DMFT while maintaining symmetric configurations. Here, we explore the hypothesis that symmetry breaking in the Kohn-Sham (KS) non-interacting system can qualitatively account for the energetic effects of strong correlation in the corresponding interacting system within standard DFT. By lifting near-degeneracies around the Fermi level, symmetry breaking diminishes the potential correlation effects, reducing the need for an explicit treatment of electron correlation, transforming an otherwise strongly correlated symmetric configuration into a normally correlated one, thus avoiding the need for interacting methods beyond DFT. This naturally connects nonmagnetic to magnetic states. We apply this idea to both strongly and normally correlated metals and observe that spin symmetry breaking leads to a pronounced reduction of the density of states at the Fermi level and a significant lowering of the total energy in strongly correlated cases. To describe the degree of correlation that the interacting system would have relative to the KS state, we introduce a correlation parameter (), defined as the ratio between the Kohn-Sham density of one-electron states at the Fermi level and that of a corresponding uniform electron gas. This parameter distinguishes strongly correlated systems, which would require explicit treatment, from normally correlated ones, which do not.},
keywords = {},
pubstate = {published},
tppubtype = {misc}
}
Strongly correlated systems have long been a central and highly non-trivial topic in condensed matter physics. At the non-interacting level, strong correlation can be associated with powerful (near) degeneracies between occupied and unoccupied states, which leads to a high density of states near the Fermi level in metallic configurations. Such regimes are commonly treated with beyond-density functional theory (DFT) approaches, such as DFT+U or DFT+DMFT while maintaining symmetric configurations. Here, we explore the hypothesis that symmetry breaking in the Kohn-Sham (KS) non-interacting system can qualitatively account for the energetic effects of strong correlation in the corresponding interacting system within standard DFT. By lifting near-degeneracies around the Fermi level, symmetry breaking diminishes the potential correlation effects, reducing the need for an explicit treatment of electron correlation, transforming an otherwise strongly correlated symmetric configuration into a normally correlated one, thus avoiding the need for interacting methods beyond DFT. This naturally connects nonmagnetic to magnetic states. We apply this idea to both strongly and normally correlated metals and observe that spin symmetry breaking leads to a pronounced reduction of the density of states at the Fermi level and a significant lowering of the total energy in strongly correlated cases. To describe the degree of correlation that the interacting system would have relative to the KS state, we introduce a correlation parameter (), defined as the ratio between the Kohn-Sham density of one-electron states at the Fermi level and that of a corresponding uniform electron gas. This parameter distinguishes strongly correlated systems, which would require explicit treatment, from normally correlated ones, which do not.
Osorio-Guillén, Jorge M.; Vélez-Vélez, John A.; Alvarez-Quiceno, Juan C.; Dalpian, Gustavo M.
Pressure-induced magnetic transition in the quasi one-dimensional quantum halide CsTiI <mml:math xmlns:mml= Journal Article
Em: Journal of Magnetism and Magnetic Materials, vol. 643, 2026, ISSN: 0304-8853.
@article{Osorio-Guillén2026,
title = {Pressure-induced magnetic transition in the quasi one-dimensional quantum halide CsTiI <mml:math xmlns:mml=},
author = {Jorge M. Osorio-Guillén and John A. Vélez-Vélez and Juan C. Alvarez-Quiceno and Gustavo M. Dalpian},
doi = {10.1016/j.jmmm.2026.173882},
issn = {0304-8853},
year = {2026},
date = {2026-04-01},
journal = {Journal of Magnetism and Magnetic Materials},
volume = {643},
publisher = {Elsevier BV},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Pereira, Gabriel X.; Farigliano, Lucas M.; Miwa, Roberto H.; Dalpian, Gustavo M.
Intrinsic Instabilities and Mechanical Anisotropy in Halide Perovskite Monolayers Miscellaneous
2026.
@misc{pereira2026intrinsicinstabilitiesmechanicalanisotropy,
title = {Intrinsic Instabilities and Mechanical Anisotropy in Halide Perovskite Monolayers},
author = {Gabriel X. Pereira and Lucas M. Farigliano and Roberto H. Miwa and Gustavo M. Dalpian},
url = {https://arxiv.org/abs/2602.21989},
year = {2026},
date = {2026-02-25},
urldate = {2026-02-25},
keywords = {},
pubstate = {published},
tppubtype = {misc}
}
Pereira, Gabriel X.; Farigliano, Lucas M.; Miwa, Roberto H.; Dalpian, Gustavo M.
Intrinsic Instabilities and Mechanical Anisotropy in Halide Perovskite Monolayers Miscellaneous
2026.
@misc{pereira2026intrinsicinstabilitiesmechanicalanisotropyb,
title = {Intrinsic Instabilities and Mechanical Anisotropy in Halide Perovskite Monolayers},
author = {Gabriel X. Pereira and Lucas M. Farigliano and Roberto H. Miwa and Gustavo M. Dalpian},
url = {https://arxiv.org/abs/2602.21989},
year = {2026},
date = {2026-02-25},
urldate = {2026-01-01},
abstract = {Halide perovskites have been extensively studied owing to their excellent optoelectronic properties and their unique lattice characteristics, that are very soft and anharmonic. Recent studies indicate the importance of a deep understanding of their surfaces and, in the limit, the properties of low-dimensional structures based on these materials. To investigate the structural and electronic properties of halide perovskite monolayers (i.e., perovskenes), this work uses first-principles simulations. We have studied three different stoichiometries (ABX3, ABX4, and A2BX4) and structural phases for iodide, bromide, and chloride perovskite monolayers. Their thermodynamic behavior was evaluated through the construction of phase diagrams, highlighting the instability of the ABX4 stoichiometry, which was further supported by its mechanical instability. Structurally, the covalent characteristics of the Pb–X bond, in contrast to the Cs–X bonds, induce a strong anisotropy in the Young's modulus and Poisson's ratio along different crystallographic directions, and also account for the lower stiffness observed in the phases where the octahedra are not aligned. The electronic properties are somewhat similar to those of their 3D counterparts, but with a slightly larger band gap; in the monolayers, the band gap increases with halogen electronegativity (I, Br, Cl) and octahedral tilting. Moreover, the non-symmetric ABX3 stoichiometry exhibited a spin splitting due to the internal dipole moment in these layers. Overall, our work lays the groundwork for a deeper understanding of low-dimensional structures based on halide perovskites.},
keywords = {},
pubstate = {published},
tppubtype = {misc}
}
Halide perovskites have been extensively studied owing to their excellent optoelectronic properties and their unique lattice characteristics, that are very soft and anharmonic. Recent studies indicate the importance of a deep understanding of their surfaces and, in the limit, the properties of low-dimensional structures based on these materials. To investigate the structural and electronic properties of halide perovskite monolayers (i.e., perovskenes), this work uses first-principles simulations. We have studied three different stoichiometries (ABX3, ABX4, and A2BX4) and structural phases for iodide, bromide, and chloride perovskite monolayers. Their thermodynamic behavior was evaluated through the construction of phase diagrams, highlighting the instability of the ABX4 stoichiometry, which was further supported by its mechanical instability. Structurally, the covalent characteristics of the Pb–X bond, in contrast to the Cs–X bonds, induce a strong anisotropy in the Young's modulus and Poisson's ratio along different crystallographic directions, and also account for the lower stiffness observed in the phases where the octahedra are not aligned. The electronic properties are somewhat similar to those of their 3D counterparts, but with a slightly larger band gap; in the monolayers, the band gap increases with halogen electronegativity (I, Br, Cl) and octahedral tilting. Moreover, the non-symmetric ABX3 stoichiometry exhibited a spin splitting due to the internal dipole moment in these layers. Overall, our work lays the groundwork for a deeper understanding of low-dimensional structures based on halide perovskites.
Braz, Lauro B.; Rivera, Daniel D.; Lopes, Emmanuel V. C.; Martins, George B.; Dalpian, Gustavo M.; Silva, Luis G. G. V. Dias
Ni-O hybridization as a stabilizer for $s^±$ superconductivity in La$_3$Ni$_2$O$_7$: a DFT+RPA study Miscellaneous
2026.
@misc{braz2026niohybridizationstabilizerspm,
title = {Ni-O hybridization as a stabilizer for $s^±$ superconductivity in La$_3$Ni$_2$O$_7$: a DFT+RPA study},
author = {Lauro B. Braz and Daniel D. Rivera and Emmanuel V. C. Lopes and George B. Martins and Gustavo M. Dalpian and Luis G. G. V. Dias Silva},
url = {https://arxiv.org/abs/2609.05185},
year = {2026},
date = {2026-01-01},
keywords = {},
pubstate = {published},
tppubtype = {misc}
}
Braz, Lauro B.; Rivera, Daniel D.; Lopes, Emmanuel V. C.; Martins, George B.; Dalpian, Gustavo M.; Silva, Luis G. G. V. Dias
Ni-O hybridization as a stabilizer for $s^±$ superconductivity in La$_3$Ni$_2$O$_7$: a DFT+RPA study Miscellaneous
2026.
@misc{braz2026niohybridizationstabilizerspmb,
title = {Ni-O hybridization as a stabilizer for $s^±$ superconductivity in La$_3$Ni$_2$O$_7$: a DFT+RPA study},
author = {Lauro B. Braz and Daniel D. Rivera and Emmanuel V. C. Lopes and George B. Martins and Gustavo M. Dalpian and Luis G. G. V. Dias Silva},
url = {https://arxiv.org/abs/2609.05185},
year = {2026},
date = {2026-01-01},
keywords = {},
pubstate = {published},
tppubtype = {misc}
}
2025
Rivera, D.; Sabino, Fernando P.; Raebiger, H.; Ruzsinszky, A.; Perdew, J. P.; Dalpian, G. M.
Exchange field induced symmetry breaking in quantum hexaborides Miscellaneous
2025.
@misc{rivera2025exchangefieldinducedsymmetry,
title = {Exchange field induced symmetry breaking in quantum hexaborides},
author = {D. Rivera and Fernando P. Sabino and H. Raebiger and A. Ruzsinszky and J. P. Perdew and G. M. Dalpian},
url = {https://arxiv.org/abs/2511.05738},
year = {2025},
date = {2025-11-07},
urldate = {2025-01-01},
abstract = {Symmetry breaking (SB) has proven to be a powerful approach for describing quantum materials: strong correlation, mass renormalization, and complex phase transitions are among the phenomena that SB can capture, even when coupled to a mean-field-like theory. Traditionally, corrective schemes were required to account for these effects; however, SB has emerged as an alternative that can also successfully describe the intricate physics of quantum materials. Here, we explore spin SB on EuB6 and SmB6 and how its relation to the exchange field can determine onsite properties, depending on the type of symmetry breaking. Using spin-polarized Density Functional Theory (DFT) calculations with the r2SCAN functional, we systematically compare four magnetic configurations, one totally symmetric - non-magnetic (NM) configuration - and three with different types of symmetry breaking: ferromagnetic (FM), antiferromagnetic (AFM) and a paramagnetic (PM) configuration - modeled through a Special Quasirandom Structure (SQS) method - to capture local symmetry-breaking effects. Our results show that the PM configuration produces distinct magnetic environments for the rare-earth atoms, leading to different exchange fields. These, in turn, induce symmetry breaking in the electronic and magnetic properties of Eu and Sm. Those results provide an alternative explanation for the experimental results on both materials, EuB6 and SmB6, where X-ray Absorption Spectroscopy (XAS) and X-ray Absorption Near Edge Structure (XANES) measurements suggest the presence of multiple atomic environments, previously attributed to a mixed-valence configuration.},
keywords = {},
pubstate = {published},
tppubtype = {misc}
}
Symmetry breaking (SB) has proven to be a powerful approach for describing quantum materials: strong correlation, mass renormalization, and complex phase transitions are among the phenomena that SB can capture, even when coupled to a mean-field-like theory. Traditionally, corrective schemes were required to account for these effects; however, SB has emerged as an alternative that can also successfully describe the intricate physics of quantum materials. Here, we explore spin SB on EuB6 and SmB6 and how its relation to the exchange field can determine onsite properties, depending on the type of symmetry breaking. Using spin-polarized Density Functional Theory (DFT) calculations with the r2SCAN functional, we systematically compare four magnetic configurations, one totally symmetric - non-magnetic (NM) configuration - and three with different types of symmetry breaking: ferromagnetic (FM), antiferromagnetic (AFM) and a paramagnetic (PM) configuration - modeled through a Special Quasirandom Structure (SQS) method - to capture local symmetry-breaking effects. Our results show that the PM configuration produces distinct magnetic environments for the rare-earth atoms, leading to different exchange fields. These, in turn, induce symmetry breaking in the electronic and magnetic properties of Eu and Sm. Those results provide an alternative explanation for the experimental results on both materials, EuB6 and SmB6, where X-ray Absorption Spectroscopy (XAS) and X-ray Absorption Near Edge Structure (XANES) measurements suggest the presence of multiple atomic environments, previously attributed to a mixed-valence configuration.
Puccinelli, Thiago; Farigliano, Lucas Martin; Dalpian, Gustavo Martini
Stability and Dynamics of Sn-based Halide Perovskites: Insights from MACE-MP-0 and Molecular Dynamics Simulations Miscellaneous
2025.
@misc{puccinelli2025stabilitydynamicssnbasedhalide,
title = {Stability and Dynamics of Sn-based Halide Perovskites: Insights from MACE-MP-0 and Molecular Dynamics Simulations},
author = {Thiago Puccinelli and Lucas Martin Farigliano and Gustavo Martini Dalpian},
url = {https://arxiv.org/abs/2510.26998},
year = {2025},
date = {2025-10-30},
urldate = {2025-01-01},
abstract = {Tin-based halide perovskites have emerged as promising lead-free alternatives for optoelectronic applications, yet their structural stability and phase behavior at finite temperatures remain challenging to predict. Here, we assess the predictive capabilities of the foundational machine learning model MACE-MP-0 - trained on a broad chemical space and applied without system-specific fine-tuning - for the temperature-dependent behavior of CsSnBr3 and Cs2SnBr6. Molecular Dynamics simulations in the NpT ensemble were performed from 100 K to 500 K, and thermodynamic and structural descriptors including enthalpy, specific heat, radial distribution functions, translational order, bond angle distributions, and vibrational spectra were analyzed. Our results show that CsSnBr3 undergoes a low-temperature orthorhombic-to-cubic phase transition, evidenced by both the evolution of lattice parameters and subtle anomalies in enthalpy and specific heat, although the experimentally observed intermediate tetragonal phase is not captured. In contrast, Cs2SnBr6 remains cubic and maintains a more rigid octahedral framework across the entire temperature range. Overall, MACE-MP-0 qualitatively reproduces key thermal and structural features of these materials, highlighting its usefulness as a first step for studying new materials. For cases where capturing more subtle phase behavior is required, system-specific fine-tuning with Density Functional Theory data should be considered.},
keywords = {},
pubstate = {published},
tppubtype = {misc}
}
Tin-based halide perovskites have emerged as promising lead-free alternatives for optoelectronic applications, yet their structural stability and phase behavior at finite temperatures remain challenging to predict. Here, we assess the predictive capabilities of the foundational machine learning model MACE-MP-0 - trained on a broad chemical space and applied without system-specific fine-tuning - for the temperature-dependent behavior of CsSnBr3 and Cs2SnBr6. Molecular Dynamics simulations in the NpT ensemble were performed from 100 K to 500 K, and thermodynamic and structural descriptors including enthalpy, specific heat, radial distribution functions, translational order, bond angle distributions, and vibrational spectra were analyzed. Our results show that CsSnBr3 undergoes a low-temperature orthorhombic-to-cubic phase transition, evidenced by both the evolution of lattice parameters and subtle anomalies in enthalpy and specific heat, although the experimentally observed intermediate tetragonal phase is not captured. In contrast, Cs2SnBr6 remains cubic and maintains a more rigid octahedral framework across the entire temperature range. Overall, MACE-MP-0 qualitatively reproduces key thermal and structural features of these materials, highlighting its usefulness as a first step for studying new materials. For cases where capturing more subtle phase behavior is required, system-specific fine-tuning with Density Functional Theory data should be considered.
Quintero, Leonardo; Miwa, R. H.; Franca, J. R.; Acuña, Jose J. S.; Dalpian, G. M.; Souza, Jose A.
Em: vol. 138, não 12, 2025, ISSN: 1089-7550.
@article{Quintero2025,
title = {Comprehensive experimental and theoretical study on the interaction between Ag nanoparticles and all-inorganic CsPb(Br,I)3 perovskite nanocrystals},
author = {Leonardo Quintero and R. H. Miwa and J. R. Franca and Jose J. S. Acuña and G. M. Dalpian and Jose A. Souza},
doi = {10.1063/5.0288333},
issn = {1089-7550},
year = {2025},
date = {2025-09-28},
urldate = {2025-09-28},
volume = {138},
number = {12},
publisher = {AIP Publishing},
abstract = {<jats:p>The energy conversion efficiency in halide perovskites remains limited by charge carrier generation, separation, mobility, and extraction. In this work, we investigate interfacial interactions governing exciton dynamics in all-inorganic CsPb(Br,I)3 nanocrystals coupled with Ag metallic nanoparticles (AgNPs). Our findings reveal strong photoluminescence (PL) quenching when AgNPs are deposited on the surface of CsPb(Br,I)3 nanocrystals, indicating the charge transfer process. A comprehensive theoretical analysis suggests that the interaction between CsX-terminated quantum dots (QDs) and AgNPs is primarily governed by weak physical adsorption van der Waals (vdW) forces, which is in contrast to PbX2 terminations, where the QD/NP interface is mediated by a combination of vdW forces and stronger chemical interactions. Our electronic structure calculations confirm the feasibility of carrier separation and the emergence of two concurrent charging processes at the QD/NP interfaces. The final charge separation configuration of QD[h]/NP[e], meaning that holes are localized in the QDs and the electrons at the nanoparticles, is more likely to occur than QD[e]/NP[h]. We discuss the electron–hole creation and separation mechanisms at the heterostructure interface, highlighting how enhanced interfacial interactions improve electronic coupling, influence optical response, and modify charge carrier dynamics. Understanding these interfacial mechanisms is essential for optimizing perovskite-based nanostructures in optoelectronics applications.</jats:p>},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
<jats:p>The energy conversion efficiency in halide perovskites remains limited by charge carrier generation, separation, mobility, and extraction. In this work, we investigate interfacial interactions governing exciton dynamics in all-inorganic CsPb(Br,I)3 nanocrystals coupled with Ag metallic nanoparticles (AgNPs). Our findings reveal strong photoluminescence (PL) quenching when AgNPs are deposited on the surface of CsPb(Br,I)3 nanocrystals, indicating the charge transfer process. A comprehensive theoretical analysis suggests that the interaction between CsX-terminated quantum dots (QDs) and AgNPs is primarily governed by weak physical adsorption van der Waals (vdW) forces, which is in contrast to PbX2 terminations, where the QD/NP interface is mediated by a combination of vdW forces and stronger chemical interactions. Our electronic structure calculations confirm the feasibility of carrier separation and the emergence of two concurrent charging processes at the QD/NP interfaces. The final charge separation configuration of QD[h]/NP[e], meaning that holes are localized in the QDs and the electrons at the nanoparticles, is more likely to occur than QD[e]/NP[h]. We discuss the electron–hole creation and separation mechanisms at the heterostructure interface, highlighting how enhanced interfacial interactions improve electronic coupling, influence optical response, and modify charge carrier dynamics. Understanding these interfacial mechanisms is essential for optimizing perovskite-based nanostructures in optoelectronics applications.</jats:p>
2024
Freitas, Andre Luiz Martins; Caturello, Naidel A. M. S.; Tofanello, Aryane; Kaneko, Ulisses F.; Correa, Lucas E.; Reis, Ricardo Donizeth; Ferreira, Fabio Furlan; Dalpian, Gustavo M.; Souza, José A
Releasing trapped excitons in 2D perovskites via pressure annealing: A cooperative interplay between lattice strain and electronic structure. Journal Article
Em: Mater. Chem. Front., 2024, ISSN: 2052-1537.
@article{deFreitas2025,
title = {Releasing trapped excitons in 2D perovskites via pressure annealing: A cooperative interplay between lattice strain and electronic structure.},
author = {Andre Luiz Martins Freitas and Naidel A. M. S. Caturello and Aryane Tofanello and Ulisses F. Kaneko and Lucas E. Correa and Ricardo Donizeth Reis and Fabio Furlan Ferreira and Gustavo M. Dalpian and José A Souza},
url = {https://pubs.rsc.org/en/content/articlelanding/2025/qm/d4qm00780h},
doi = {10.1039/d4qm00780h},
issn = {2052-1537},
year = {2024},
date = {2024-12-11},
journal = {Mater. Chem. Front.},
publisher = {Royal Society of Chemistry (RSC)},
abstract = {The characteristic photon emissions in low-dimensional hybrid perovskites are strongly related to inherent distortions in the crystal lattice. These cooperative distortions, influenced by organic spacers and the confined BX6 octahedra arrangement, allow for the manipulation and control of the emitted photon energy and its nature. Here, we observe a complex dynamic where photon emissions at both low and high energies emerge, depending on octahedral distortion and the application of hydrostatic pressure. Our results demonstrate that samples featuring different octahedra sizes and distortions, yet having a common organic spacer (BA2MAPb2Br7 and BA2MAPb2I7), show low-energy photon emission attributed to self-trapped excitons (STEs) which can be tuned towards to free exciton states (FE) through pressure annealing. Experimental and theoretical results revealed that octahedral distortions in 2D perovskites play a crucial role in controlling emission, disclosing their complex structure and electronic relationship.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The characteristic photon emissions in low-dimensional hybrid perovskites are strongly related to inherent distortions in the crystal lattice. These cooperative distortions, influenced by organic spacers and the confined BX6 octahedra arrangement, allow for the manipulation and control of the emitted photon energy and its nature. Here, we observe a complex dynamic where photon emissions at both low and high energies emerge, depending on octahedral distortion and the application of hydrostatic pressure. Our results demonstrate that samples featuring different octahedra sizes and distortions, yet having a common organic spacer (BA2MAPb2Br7 and BA2MAPb2I7), show low-energy photon emission attributed to self-trapped excitons (STEs) which can be tuned towards to free exciton states (FE) through pressure annealing. Experimental and theoretical results revealed that octahedral distortions in 2D perovskites play a crucial role in controlling emission, disclosing their complex structure and electronic relationship.
Sabino, Fernando P.; Zhao, Xin Gang; Dalpian, Gustavo M.; Zunger, Alex
Impact of symmetry breaking and spin-orbit coupling on the band gap of halide perovskites Journal Article
Em: Phys. Rev. B, vol. 110, iss. 3, pp. 035160, 2024.
@article{PhysRevB.110.035160,
title = {Impact of symmetry breaking and spin-orbit coupling on the band gap of halide perovskites},
author = {Fernando P. Sabino and Xin Gang Zhao and Gustavo M. Dalpian and Alex Zunger},
url = {https://link.aps.org/doi/10.1103/PhysRevB.110.035160},
doi = {10.1103/PhysRevB.110.035160},
year = {2024},
date = {2024-07-30},
urldate = {2024-07-01},
journal = {Phys. Rev. B},
volume = {110},
issue = {3},
pages = {035160},
publisher = {American Physical Society},
abstract = {Halide perovskite (HP) materials have recently emerged as a class of semiconductors with immense promise for various optoelectronic applications, ranging from solar cells to light-emitting diodes. One of the unique attributes of HPs is their tunable band gaps with different factors governing their value. The first factor is related to relativistic corrections [“mass-Darwin,” connected to the 𝑛𝑠2 lone pairs, and spin-orbit coupling (SOC)] that induce an orbital shift or degeneracy splitting, resulting in a band-gap reduction. The second factor involves the structural configuration: in HPs the local symmetry of each Wyckoff position tends to be broken, inducing an opening of the band gap. Based on high-throughput density functional theory calculations, this paper systematically studies a possible self-cancelation on the band-gap correction for HPs when the polymorphous configuration—structural effects—and the SOC—electronic effects—are included. Our results indicate that the nature of interplay between SOC and symmetry breaking (SB) is that they are independent decoupling effects to describe the band-gap magnitude in halide perovskites. As a result of that, we observe a transitivity of the band-gap description; i.e., if we know the band gap of halide perovskites without SB and SOC, we can independently add the effects of band-gap reduction due to SOC and band-gap opening due to SB, regardless of the order in which these effects are considered.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Halide perovskite (HP) materials have recently emerged as a class of semiconductors with immense promise for various optoelectronic applications, ranging from solar cells to light-emitting diodes. One of the unique attributes of HPs is their tunable band gaps with different factors governing their value. The first factor is related to relativistic corrections [“mass-Darwin,” connected to the 𝑛𝑠2 lone pairs, and spin-orbit coupling (SOC)] that induce an orbital shift or degeneracy splitting, resulting in a band-gap reduction. The second factor involves the structural configuration: in HPs the local symmetry of each Wyckoff position tends to be broken, inducing an opening of the band gap. Based on high-throughput density functional theory calculations, this paper systematically studies a possible self-cancelation on the band-gap correction for HPs when the polymorphous configuration—structural effects—and the SOC—electronic effects—are included. Our results indicate that the nature of interplay between SOC and symmetry breaking (SB) is that they are independent decoupling effects to describe the band-gap magnitude in halide perovskites. As a result of that, we observe a transitivity of the band-gap description; i.e., if we know the band gap of halide perovskites without SB and SOC, we can independently add the effects of band-gap reduction due to SOC and band-gap opening due to SB, regardless of the order in which these effects are considered.
Farigliano, Lucas M.; Negreiros, Fabio R.; Dalpian, Gustavo M.
Phase Transitions of CsPbBr3: Evaluating Perovskite Behavior Over Different Time Scales Journal Article
Em: Mater. Adv., pp. -, 2024.
@article{D4MA00216D,
title = {Phase Transitions of CsPbBr3: Evaluating Perovskite Behavior Over Different Time Scales},
author = {Lucas M. Farigliano and Fabio R. Negreiros and Gustavo M. Dalpian},
url = {http://dx.doi.org/10.1039/D4MA00216D},
doi = {10.1039/D4MA00216D},
year = {2024},
date = {2024-06-04},
urldate = {2024-01-01},
journal = {Mater. Adv.},
pages = {-},
publisher = {RSC},
abstract = {Halide perovskites have gained relevance in the field of solar cells due to their remarkable electro-optical properties, which enable efficient conversion of solar energy into electricity. Despite their promising characteristics, challenges such as long-term stability and structural complexity demand exceptional attention and dedication in the research on these materials. Their inherent soft nature, high atom mobility (especially of the halides) and the unconventional dynamics of structural motifs (halide octahedra) make them interesting from a fundamental point of view as well. The study focuses on understanding phase transitions in CsPbBr3 perovskite, considering the importance of the dynamic properties it exhibits. The phase transitions of the CsPbBr3 perovskite were studied through ab initio NPT molecular dynamics simulations considering several different temperatures. By taking into account the average structures over a simulation time of 45 ps after thermalization, we predict phase transitions between 300 and 325 K, as well as between 400 and 450 K, in line with previous experimental findings reported in the literature. Furthermore, through the analysis of the angles within the octahedron (Br-Pb-Br) and between octahedra (Pb-Br-Pb), the mechanism underlying the phase transitions is understood, and the structural anomalies previously reported [Svirskas et al., Journal of Materials Chemistry A, 2020, 8, 3523] near 220 K are identified. In addition to the results obtained by performing long-time averages, we also conducted an analysis of the implications of using different time windows when calculating the average properties of interest. In this case, we observed a more complex pattern, where the material exhibits various structures depending on the exposure time and temperature, which aligns with the polymorphic nature of these materials. Our results show that, depending on the type of experiment that is being performed, different analysis, with averages considered over different times, must be performed. Long-time averages can be compared to x-ray diffraction experiments, while short-time averages should be compared to experiments that track the local structure of the material, such as PDF or Raman. Our results also indicate that phase transitions in CsPbBr3 are not as abrupt as previously considered, posing new challenges for the experimental observation of these features.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Halide perovskites have gained relevance in the field of solar cells due to their remarkable electro-optical properties, which enable efficient conversion of solar energy into electricity. Despite their promising characteristics, challenges such as long-term stability and structural complexity demand exceptional attention and dedication in the research on these materials. Their inherent soft nature, high atom mobility (especially of the halides) and the unconventional dynamics of structural motifs (halide octahedra) make them interesting from a fundamental point of view as well. The study focuses on understanding phase transitions in CsPbBr3 perovskite, considering the importance of the dynamic properties it exhibits. The phase transitions of the CsPbBr3 perovskite were studied through ab initio NPT molecular dynamics simulations considering several different temperatures. By taking into account the average structures over a simulation time of 45 ps after thermalization, we predict phase transitions between 300 and 325 K, as well as between 400 and 450 K, in line with previous experimental findings reported in the literature. Furthermore, through the analysis of the angles within the octahedron (Br-Pb-Br) and between octahedra (Pb-Br-Pb), the mechanism underlying the phase transitions is understood, and the structural anomalies previously reported [Svirskas et al., Journal of Materials Chemistry A, 2020, 8, 3523] near 220 K are identified. In addition to the results obtained by performing long-time averages, we also conducted an analysis of the implications of using different time windows when calculating the average properties of interest. In this case, we observed a more complex pattern, where the material exhibits various structures depending on the exposure time and temperature, which aligns with the polymorphic nature of these materials. Our results show that, depending on the type of experiment that is being performed, different analysis, with averages considered over different times, must be performed. Long-time averages can be compared to x-ray diffraction experiments, while short-time averages should be compared to experiments that track the local structure of the material, such as PDF or Raman. Our results also indicate that phase transitions in CsPbBr3 are not as abrupt as previously considered, posing new challenges for the experimental observation of these features.
Ogoshi, Elton; Popolin-Neto, Mário; Acosta, Carlos Mera; Nascimento, Gabriel M.; Rodrigues, João N. B.; Oliveira, Osvaldo N.; Paulovich, Fernando V.; Dalpian, Gustavo M.
Learning from machine learning: the case of band-gap directness in semiconductors Journal Article
Em: Discov Mater, vol. 4, não 1, 2024, ISSN: 2730-7727.
@article{Ogoshi2024,
title = {Learning from machine learning: the case of band-gap directness in semiconductors},
author = {Elton Ogoshi and Mário Popolin-Neto and Carlos Mera Acosta and Gabriel M. Nascimento and João N. B. Rodrigues and Osvaldo N. Oliveira and Fernando V. Paulovich and Gustavo M. Dalpian},
url = {https://link.springer.com/article/10.1007/s43939-024-00073-x},
doi = {10.1007/s43939-024-00073-x},
issn = {2730-7727},
year = {2024},
date = {2024-02-29},
journal = {Discov Mater},
volume = {4},
number = {1},
publisher = {Springer Science and Business Media LLC},
abstract = {<jats:title>Abstract</jats:title><jats:p>Having a direct or indirect band gap can influence the potential applications of a semiconductor, for indirect band gap materials are usually not suitable for optoelectronic devices. Even though this is a fundamental property of semiconducting materials, discussed in textbooks, no unified theory exists to explain why a material has a direct or indirect band gap. Here we used an interpretable machine learning model, the multiVariate dAta eXplanation (VAX) method, to gather information from a dataset of materials extracted from the Materials Project. The dataset contains more than 10000 entries, and atomic properties such as the number of electrons, electronic affinity and orbital energies were used as features to build random forest models that successfully explain the directness of the band gaps. Our results indicate that symmetry is an important feature that dictates the target property, which is the reason why our analysis is made based on sub-groups with similar structures. These sub-groups include materials with zincblende, rocksalt, wurtzite, and perovskite structures. Besides the symmetry of the materials, the existence or not of <jats:italic>d</jats:italic> bands and the relative energy of atomic orbitals were found to be important in defining whether a material’s band gap is direct or indirect. In conclusion, interpretable machine learning methods such as VAX can be useful in obtaining physical interpretation from materials databases.</jats:p>},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
<jats:title>Abstract</jats:title><jats:p>Having a direct or indirect band gap can influence the potential applications of a semiconductor, for indirect band gap materials are usually not suitable for optoelectronic devices. Even though this is a fundamental property of semiconducting materials, discussed in textbooks, no unified theory exists to explain why a material has a direct or indirect band gap. Here we used an interpretable machine learning model, the multiVariate dAta eXplanation (VAX) method, to gather information from a dataset of materials extracted from the Materials Project. The dataset contains more than 10000 entries, and atomic properties such as the number of electrons, electronic affinity and orbital energies were used as features to build random forest models that successfully explain the directness of the band gaps. Our results indicate that symmetry is an important feature that dictates the target property, which is the reason why our analysis is made based on sub-groups with similar structures. These sub-groups include materials with zincblende, rocksalt, wurtzite, and perovskite structures. Besides the symmetry of the materials, the existence or not of <jats:italic>d</jats:italic> bands and the relative energy of atomic orbitals were found to be important in defining whether a material’s band gap is direct or indirect. In conclusion, interpretable machine learning methods such as VAX can be useful in obtaining physical interpretation from materials databases.</jats:p>
Ogoshi, Elton; Popolin-Neto, Mário; Acosta, Carlos Mera; Nascimento, Gabriel M.; Rodrigues, João N. B.; Oliveira, Osvaldo N.; Paulovich, Fernando V.; Dalpian, Gustavo M.
Learning from machine learning: the case of band-gap directness in semiconductors Journal Article
Em: Discov Mater, vol. 4, não 1, 2024, ISSN: 2730-7727.
@article{Ogoshi2024b,
title = {Learning from machine learning: the case of band-gap directness in semiconductors},
author = {Elton Ogoshi and Mário Popolin-Neto and Carlos Mera Acosta and Gabriel M. Nascimento and João N. B. Rodrigues and Osvaldo N. Oliveira and Fernando V. Paulovich and Gustavo M. Dalpian},
url = {https://repositorio.usp.br/directbitstream/1ee44f9f-13de-45ad-bb4b-fb7f0cb95272/3183025%20falta%20rep.pdf},
doi = {10.1007/s43939-024-00073-x},
issn = {2730-7727},
year = {2024},
date = {2024-02-29},
journal = {Discov Mater},
volume = {4},
number = {1},
publisher = {Springer Science and Business Media LLC},
abstract = {<jats:title>Abstract</jats:title><jats:p>Having a direct or indirect band gap can influence the potential applications of a semiconductor, for indirect band gap materials are usually not suitable for optoelectronic devices. Even though this is a fundamental property of semiconducting materials, discussed in textbooks, no unified theory exists to explain why a material has a direct or indirect band gap. Here we used an interpretable machine learning model, the multiVariate dAta eXplanation (VAX) method, to gather information from a dataset of materials extracted from the Materials Project. The dataset contains more than 10000 entries, and atomic properties such as the number of electrons, electronic affinity and orbital energies were used as features to build random forest models that successfully explain the directness of the band gaps. Our results indicate that symmetry is an important feature that dictates the target property, which is the reason why our analysis is made based on sub-groups with similar structures. These sub-groups include materials with zincblende, rocksalt, wurtzite, and perovskite structures. Besides the symmetry of the materials, the existence or not of <jats:italic>d</jats:italic> bands and the relative energy of atomic orbitals were found to be important in defining whether a material’s band gap is direct or indirect. In conclusion, interpretable machine learning methods such as VAX can be useful in obtaining physical interpretation from materials databases.</jats:p>},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
<jats:title>Abstract</jats:title><jats:p>Having a direct or indirect band gap can influence the potential applications of a semiconductor, for indirect band gap materials are usually not suitable for optoelectronic devices. Even though this is a fundamental property of semiconducting materials, discussed in textbooks, no unified theory exists to explain why a material has a direct or indirect band gap. Here we used an interpretable machine learning model, the multiVariate dAta eXplanation (VAX) method, to gather information from a dataset of materials extracted from the Materials Project. The dataset contains more than 10000 entries, and atomic properties such as the number of electrons, electronic affinity and orbital energies were used as features to build random forest models that successfully explain the directness of the band gaps. Our results indicate that symmetry is an important feature that dictates the target property, which is the reason why our analysis is made based on sub-groups with similar structures. These sub-groups include materials with zincblende, rocksalt, wurtzite, and perovskite structures. Besides the symmetry of the materials, the existence or not of <jats:italic>d</jats:italic> bands and the relative energy of atomic orbitals were found to be important in defining whether a material’s band gap is direct or indirect. In conclusion, interpretable machine learning methods such as VAX can be useful in obtaining physical interpretation from materials databases.</jats:p>
Morais, Eliane A.; Caturello, Naidel A. M. S.; Lemes, Maykon A.; Ferreira, Henrique; Ferreira, Fabio F.; Acuña, Jose J. S.; Brochsztain, Sergio; Dalpian, Gustavo M.; Souza, Jose A.
Rashba Spin Splitting Limiting the Application of 2D Halide Perovskites for UV-Emitting Devices Journal Article
Em: ACS Applied Materials & Interfaces, vol. 0, não 0, pp. null, 2024, (PMID: 38217498).
@article{doi:10.1021/acsami.3c16541,
title = {Rashba Spin Splitting Limiting the Application of 2D Halide Perovskites for UV-Emitting Devices},
author = {Eliane A. Morais and Naidel A. M. S. Caturello and Maykon A. Lemes and Henrique Ferreira and Fabio F. Ferreira and Jose J. S. Acuña and Sergio Brochsztain and Gustavo M. Dalpian and Jose A. Souza},
url = {https://doi.org/10.1021/acsami.3c16541},
doi = {10.1021/acsami.3c16541},
year = {2024},
date = {2024-01-13},
journal = {ACS Applied Materials & Interfaces},
volume = {0},
number = {0},
pages = {null},
abstract = {Layered lead halide perovskites have attracted much attention as promising materials for a new generation of optoelectronic devices. To make progress in applications, a full understanding of the basic properties is essential. Here, we study 2D-layered (BA)2PbX4 by using different halide anions (X = I, Br, and Cl) along with quantum confinement. The obtained cell parameter evolution, supported by experimental measurements and theoretical calculations, indicates strong lattice distortions of the metal halide octahedra, breaking the local inversion symmetry in (BA)2PbCl4, which strongly correlates with a pronounced Rashba spin-splitting effect. Optical measurements reveal strong photoluminescence quenching and a drastic reduction in the PL quantum yield in this larger band gap compound. We suggest that these optical results are closely related to the appearance of the Rashba effect due to the existence of a local electric dipole. The results obtained in ab initio calculations showed that the (BA)2PbCl4 possesses electrical polarization of 0.13 μC/cm2 and spin-splitting energy of about 40 meV. Our work establishes that local octahedra distortions induce Rashba spin splitting, which explains why obtaining UV-emitting materials with high PLQY is a big challenge.},
note = {PMID: 38217498},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Layered lead halide perovskites have attracted much attention as promising materials for a new generation of optoelectronic devices. To make progress in applications, a full understanding of the basic properties is essential. Here, we study 2D-layered (BA)2PbX4 by using different halide anions (X = I, Br, and Cl) along with quantum confinement. The obtained cell parameter evolution, supported by experimental measurements and theoretical calculations, indicates strong lattice distortions of the metal halide octahedra, breaking the local inversion symmetry in (BA)2PbCl4, which strongly correlates with a pronounced Rashba spin-splitting effect. Optical measurements reveal strong photoluminescence quenching and a drastic reduction in the PL quantum yield in this larger band gap compound. We suggest that these optical results are closely related to the appearance of the Rashba effect due to the existence of a local electric dipole. The results obtained in ab initio calculations showed that the (BA)2PbCl4 possesses electrical polarization of 0.13 μC/cm2 and spin-splitting energy of about 40 meV. Our work establishes that local octahedra distortions induce Rashba spin splitting, which explains why obtaining UV-emitting materials with high PLQY is a big challenge.
2023
Sabino, Fernando P.; Dalpian, Gustavo M.; Zunger, Alex
Light-Induced Frenkel Defect Pair Formation Can Lead to Phase-Segregation of Otherwise Miscible Halide Perovskite Alloys Journal Article
Em: Advanced Energy Materials, vol. n/a, não n/a, pp. 2301539, 2023.
@article{https://doi.org/10.1002/aenm.202301539,
title = {Light-Induced Frenkel Defect Pair Formation Can Lead to Phase-Segregation of Otherwise Miscible Halide Perovskite Alloys},
author = {Fernando P. Sabino and Gustavo M. Dalpian and Alex Zunger},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/aenm.202301539},
doi = {https://doi.org/10.1002/aenm.202301539},
year = {2023},
date = {2023-10-11},
journal = {Advanced Energy Materials},
volume = {n/a},
number = {n/a},
pages = {2301539},
abstract = {Abstract Alloys of ABX3 halide perovskites (HP) exhibit unique phase behavior compared to traditional III-V and II-VI semiconductor alloys used in solar cells. While the latter typically have good mutual miscibility when their mixed components are size matched, and phase-segregate when size mismatched, HP alloys show good miscibility in the dark but can phase-segregate under light. Quantum mechanical calculations described herein reveal light-induced defect formation and migration hold the key. Specifically, the interaction between a halogen vacancy VX with halogen interstitial Xi forming together a Frenkel-pair defect emerges as the enabler for phase-segregation in HP alloys. At a threshold bromine composition in the Br-I alloys, the photogenerated holes in the valence band localize, creating thereby a doubly-charged iodine Frenkel-pair (VI + Ii)2+. Faster migration of iodine over bromine interstitial into the vacant iodine VI site leads to the formation of iodine-rich and iodine-depleted regions, establishing phase-segregation. Removal of the mobile defects–the agent of segregation–by dark thermal annealing, supplies the opposing force, leading to reversal of phase-segregation. This atomistic understanding can enable some control of the phase-segregation by selecting substituting elements on the B site–such as replacing some Pb by Sn–that are unable to form stable Frenkel defects.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract Alloys of ABX3 halide perovskites (HP) exhibit unique phase behavior compared to traditional III-V and II-VI semiconductor alloys used in solar cells. While the latter typically have good mutual miscibility when their mixed components are size matched, and phase-segregate when size mismatched, HP alloys show good miscibility in the dark but can phase-segregate under light. Quantum mechanical calculations described herein reveal light-induced defect formation and migration hold the key. Specifically, the interaction between a halogen vacancy VX with halogen interstitial Xi forming together a Frenkel-pair defect emerges as the enabler for phase-segregation in HP alloys. At a threshold bromine composition in the Br-I alloys, the photogenerated holes in the valence band localize, creating thereby a doubly-charged iodine Frenkel-pair (VI + Ii)2+. Faster migration of iodine over bromine interstitial into the vacant iodine VI site leads to the formation of iodine-rich and iodine-depleted regions, establishing phase-segregation. Removal of the mobile defects–the agent of segregation–by dark thermal annealing, supplies the opposing force, leading to reversal of phase-segregation. This atomistic understanding can enable some control of the phase-segregation by selecting substituting elements on the B site–such as replacing some Pb by Sn–that are unable to form stable Frenkel defects.
Espinosa-García, W. F.; Dalpian, Gustavo M.; Osorio-Guillén, J. M.
Intrinsic defects in sulvanite compounds: the case of transparent Cu3TaS4 and absorbing Cu3VSe4 Journal Article
Em: Journal of Alloys and Compounds, pp. 172264, 2023, ISSN: 0925-8388.
@article{ESPINOSAGARCIA2023172264,
title = {Intrinsic defects in sulvanite compounds: the case of transparent Cu3TaS4 and absorbing Cu3VSe4},
author = {W. F. Espinosa-García and Gustavo M. Dalpian and J. M. Osorio-Guillén},
url = {https://www.sciencedirect.com/science/article/pii/S0925838823035673},
doi = {https://doi.org/10.1016/j.jallcom.2023.172264},
issn = {0925-8388},
year = {2023},
date = {2023-09-25},
urldate = {2023-01-01},
journal = {Journal of Alloys and Compounds},
pages = {172264},
abstract = {Sulvanites are semiconducting compounds with the chemical formula Cu3TMX4 where TM = V, Nb, Ta; X = S, Se, Te. Semiconductor electronic and optical properties are highly influenced by intrinsic defects such as vacancies, antisites, and atoms residing in interstitial positions inside the crystal structure. Even though intrinsic defects are extremely important, very little is known about defects in sulvanites. Here we report the properties of all intrinsic defects in two representative sulvanite compounds (Cu3TaS4 and Cu3VSe4) by using computational quantum mechanical methods. Our results indicate that Cu vacancies are the most frequent defects in these compounds, also responsible for limiting the possibility of their n-type doping and setting the pinning of the Fermi energy to positions close to the valence band. These results explain why as-grown sulvanites are usually p-type and open a path for understanding the search for ways to design and tune the properties of these compounds.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Sulvanites are semiconducting compounds with the chemical formula Cu3TMX4 where TM = V, Nb, Ta; X = S, Se, Te. Semiconductor electronic and optical properties are highly influenced by intrinsic defects such as vacancies, antisites, and atoms residing in interstitial positions inside the crystal structure. Even though intrinsic defects are extremely important, very little is known about defects in sulvanites. Here we report the properties of all intrinsic defects in two representative sulvanite compounds (Cu3TaS4 and Cu3VSe4) by using computational quantum mechanical methods. Our results indicate that Cu vacancies are the most frequent defects in these compounds, also responsible for limiting the possibility of their n-type doping and setting the pinning of the Fermi energy to positions close to the valence band. These results explain why as-grown sulvanites are usually p-type and open a path for understanding the search for ways to design and tune the properties of these compounds.
Sabino, Fernando; Zhao, Xingang; Dalpian, Gustavo M.; Zunger, Alex
Correlation between band gap shifts due to symmetry breaking and spin-orbital coupling in halide perovskites Working paper
2023.
@workingpaper{2023APS..MARS41008S,
title = {Correlation between band gap shifts due to symmetry breaking and spin-orbital coupling in halide perovskites},
author = {Fernando Sabino and Xingang Zhao and Gustavo M. Dalpian and Alex Zunger},
url = {https://ui.adsabs.harvard.edu/abs/2023APS..MARS41008S/abstract},
year = {2023},
date = {2023-02-13},
urldate = {2023-01-01},
booktitle = {APS March Meeting Abstracts},
volume = {2023},
pages = {S41.008},
series = {APS Meeting Abstracts},
abstract = {The calculation of band gaps of Halide perovskites (HP) differs from analogous calculations of more conventional semiconductors in that two additional factors need to be considered: (i) creation of a structural polymorphous network (a distribution of octahedral titling for different octahedra in cubic structures) - which increase the band gaps and (ii) spin-orbital coupling (SOC) - generally reducing the band gaps for compounds with high Z atoms. This raises the question to what extent effects (i) and (ii) compensate each other or if they are correlated in some way. We addressed this question by a series of DFT band structure calculations on cubic ABX3 compounds where effects (i) and (ii) are both included; or both excluded, or including one at the time. For the most studied inorganic halide perovskites, the SOC - induced band gap reduction has a low correlation with the band gap increase due to polymorphous network formation. The accuracy of treating the gap shifts due to (i) and (ii) as independent corrections for nominal cubic Pm-3m structures will be presented and discussed.},
keywords = {},
pubstate = {published},
tppubtype = {workingpaper}
}
The calculation of band gaps of Halide perovskites (HP) differs from analogous calculations of more conventional semiconductors in that two additional factors need to be considered: (i) creation of a structural polymorphous network (a distribution of octahedral titling for different octahedra in cubic structures) - which increase the band gaps and (ii) spin-orbital coupling (SOC) - generally reducing the band gaps for compounds with high Z atoms. This raises the question to what extent effects (i) and (ii) compensate each other or if they are correlated in some way. We addressed this question by a series of DFT band structure calculations on cubic ABX3 compounds where effects (i) and (ii) are both included; or both excluded, or including one at the time. For the most studied inorganic halide perovskites, the SOC - induced band gap reduction has a low correlation with the band gap increase due to polymorphous network formation. The accuracy of treating the gap shifts due to (i) and (ii) as independent corrections for nominal cubic Pm-3m structures will be presented and discussed.
Padilha, Antonio Claudio Michejevs; Rocha, Alexandre Reily; Dalpian, Gustavo M.
17 - Ordered vacancy compounds: the case of the Mangéli phases of TiO2 Book Section
Em: Kumar, Vijay; Som, Sudipta; Sharma, Vishal; Swart, Hendrik C. (Ed.): Metal Oxide Defects, pp. 533-565, Elsevier, 2023, ISBN: 978-0-323-85588-4.
@incollection{MICHEJEVSPADILHA2023533,
title = {17 - Ordered vacancy compounds: the case of the Mangéli phases of TiO2},
author = {Antonio Claudio Michejevs Padilha and Alexandre Reily Rocha and Gustavo M. Dalpian},
editor = {Vijay Kumar and Sudipta Som and Vishal Sharma and Hendrik C. Swart},
url = {https://www.sciencedirect.com/science/article/pii/B9780323855884000143},
doi = {https://doi.org/10.1016/B978-0-323-85588-4.00014-3},
isbn = {978-0-323-85588-4},
year = {2023},
date = {2023-01-01},
urldate = {2023-01-01},
booktitle = {Metal Oxide Defects},
pages = {533-565},
publisher = {Elsevier},
series = {Metal Oxides},
abstract = {Defects typically appear in materials in very limited quantities, usually of the order of 1016–1019/cm3. In some cases, however, these defects can be observed in a much larger concentration, enough to change the stoichiometry of the parent compound and even change their crystal structure. An important class of these materials is the ordered vacancy compounds, first proposed for CdIn2Se4. Other compounds, such as hybrid perovskites, can also present ordered vacancy compounds, such as Cs2SnI6, derived from CsSnI3. In this chapter, we will discuss ordered vacancy compounds derived from the transition metal oxide compound TiO2. These are known as the Magnéli phases of TiO2 and can be constructed by removing oxygen atoms from the host lattice. There are several different polymorphs that can be created by changing the quantity of oxygen vacancies, including Ti2O3, Ti3O5, and Ti4O7 (based on the formula TinO2n−1). We will discuss the structural determination of these materials that can be created by sliding planes from the rutile TiO2 structure. Also, the electronic structure of these compounds is characteristic of intermediate band materials and can be directly correlated to the properties of oxygen vacancies in TiO2. Lastly, we will discuss the potential applications of this kind of materials that can include memristors and batteries.},
keywords = {},
pubstate = {published},
tppubtype = {incollection}
}
Defects typically appear in materials in very limited quantities, usually of the order of 1016–1019/cm3. In some cases, however, these defects can be observed in a much larger concentration, enough to change the stoichiometry of the parent compound and even change their crystal structure. An important class of these materials is the ordered vacancy compounds, first proposed for CdIn2Se4. Other compounds, such as hybrid perovskites, can also present ordered vacancy compounds, such as Cs2SnI6, derived from CsSnI3. In this chapter, we will discuss ordered vacancy compounds derived from the transition metal oxide compound TiO2. These are known as the Magnéli phases of TiO2 and can be constructed by removing oxygen atoms from the host lattice. There are several different polymorphs that can be created by changing the quantity of oxygen vacancies, including Ti2O3, Ti3O5, and Ti4O7 (based on the formula TinO2n−1). We will discuss the structural determination of these materials that can be created by sliding planes from the rutile TiO2 structure. Also, the electronic structure of these compounds is characteristic of intermediate band materials and can be directly correlated to the properties of oxygen vacancies in TiO2. Lastly, we will discuss the potential applications of this kind of materials that can include memristors and batteries.
Bonadio, Ariany; Sabino, Fernando P.; Freitas, André L. M.; Felez, Marissol R.; Dalpian, Gustavo M.; Souza, Jose A.
Comparing the Cubic and Tetragonal Phases of MAPbI3 at Room Temperature Journal Article
Em: Inorganic Chemistry, vol. 62, não 19, pp. 7533-7544, 2023, (PMID: 37126785).
@article{doi:10.1021/acs.inorgchem.3c00874,
title = {Comparing the Cubic and Tetragonal Phases of MAPbI3 at Room Temperature},
author = {Ariany Bonadio and Fernando P. Sabino and André L. M. Freitas and Marissol R. Felez and Gustavo M. Dalpian and Jose A. Souza},
url = {https://doi.org/10.1021/acs.inorgchem.3c00874},
doi = {10.1021/acs.inorgchem.3c00874},
year = {2023},
date = {2023-01-01},
journal = {Inorganic Chemistry},
volume = {62},
number = {19},
pages = {7533-7544},
abstract = {Stability and maintenance of the crystal structure are the main drawbacks of the application of organic–inorganic perovskites in photovoltaic devices. The ΔT = 62 K robust shift of the structural phase transition observed here allows us to conduct a comprehensive study at room temperature of the tetragonal versus cubic phase on MAPbI3. The absence of the shift in the cubic transition for all-inorganic CsPbI3 samples confirms the importance of both orientation and dynamics of the organic cations. Our results provide a unique opportunity to evaluate the physical properties of both cubic and tetragonal phases of MAPbI3 at the same temperature, eliminating different phonon effects as possible causes for different properties. Besides higher electrical resistivity, the perovskite cubic phase presents a faster charge carrier lifetime than the tetragonal phase and partial PL quenching, pointing toward increased trap-assisted nonradiative recombination. The light absorption coefficient in the cubic phase is larger than the absorption in the tetragonal phase in the green region.},
note = {PMID: 37126785},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Stability and maintenance of the crystal structure are the main drawbacks of the application of organic–inorganic perovskites in photovoltaic devices. The ΔT = 62 K robust shift of the structural phase transition observed here allows us to conduct a comprehensive study at room temperature of the tetragonal versus cubic phase on MAPbI3. The absence of the shift in the cubic transition for all-inorganic CsPbI3 samples confirms the importance of both orientation and dynamics of the organic cations. Our results provide a unique opportunity to evaluate the physical properties of both cubic and tetragonal phases of MAPbI3 at the same temperature, eliminating different phonon effects as possible causes for different properties. Besides higher electrical resistivity, the perovskite cubic phase presents a faster charge carrier lifetime than the tetragonal phase and partial PL quenching, pointing toward increased trap-assisted nonradiative recombination. The light absorption coefficient in the cubic phase is larger than the absorption in the tetragonal phase in the green region.
Freitas, Andre Luiz Martins; Tofanello, Aryane; Sabino, Fernando Pereira; Felez, Marissol Rodrigues; Morais, Eliane Aparecida; Brochsztain, Sergio; Acuña, Jose Javier Sáez; Dalpian, Gustavo M.; Souza, Jose Antonio
Finite-Size Effects on Cs3Cu2I5 0D Electronic Nanostructures for Ultraviolet-Emitting Applications Journal Article
Em: ACS Applied Nano Materials, vol. 6, não 9, pp. 7196-7205, 2023.
@article{doi:10.1021/acsanm.3c00242,
title = {Finite-Size Effects on Cs3Cu2I5 0D Electronic Nanostructures for Ultraviolet-Emitting Applications},
author = {Andre Luiz Martins Freitas and Aryane Tofanello and Fernando Pereira Sabino and Marissol Rodrigues Felez and Eliane Aparecida Morais and Sergio Brochsztain and Jose Javier Sáez Acuña and Gustavo M. Dalpian and Jose Antonio Souza},
url = {https://doi.org/10.1021/acsanm.3c00242},
doi = {10.1021/acsanm.3c00242},
year = {2023},
date = {2023-01-01},
urldate = {2023-01-01},
journal = {ACS Applied Nano Materials},
volume = {6},
number = {9},
pages = {7196-7205},
abstract = {The potential to produce ultraviolet (UV) light-emitting devices has attracted significant interest in interdisciplinary fields, particularly in the use of 0D halide nanostructures due to their straightforward synthesis methods and exceptional efficiency in optoelectronics. Here, we present a systematic study involving nanostructure synthesis and significant changes in the electronic structure caused by finite-size effects. We have focused on the investigation of size effects on the UV-light emitting properties of all-inorganic Cs3Cu2I5 halide. We observe that bulk particles present a pronounced bright-blue emission at 440 nm with a high quantum yield of 80%. Very small quantum dots nanostructures (6–10 nm) reveal a significant shift of the photoluminescence peak down to ∼395 nm, close to the UV-A region, but with a quantum yield reduction of 10%. Surface engineering to obtain very small nanoparticles free from defects at the nanocrystal surface is crucial for maintaining a high quantum efficiency, allowing their use in UV-emitting devices.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The potential to produce ultraviolet (UV) light-emitting devices has attracted significant interest in interdisciplinary fields, particularly in the use of 0D halide nanostructures due to their straightforward synthesis methods and exceptional efficiency in optoelectronics. Here, we present a systematic study involving nanostructure synthesis and significant changes in the electronic structure caused by finite-size effects. We have focused on the investigation of size effects on the UV-light emitting properties of all-inorganic Cs3Cu2I5 halide. We observe that bulk particles present a pronounced bright-blue emission at 440 nm with a high quantum yield of 80%. Very small quantum dots nanostructures (6–10 nm) reveal a significant shift of the photoluminescence peak down to ∼395 nm, close to the UV-A region, but with a quantum yield reduction of 10%. Surface engineering to obtain very small nanoparticles free from defects at the nanocrystal surface is crucial for maintaining a high quantum efficiency, allowing their use in UV-emitting devices.
Ogoshi, Elton; Ferreira, Henrique; Rodrigues, João N. B.; Dalpian, Gustavo M.
Exploring chemical compound space with a graph-based recommender system Working paper
2023.
@workingpaper{ogoshi2023exploring,
title = {Exploring chemical compound space with a graph-based recommender system},
author = {Elton Ogoshi and Henrique Ferreira and João N. B. Rodrigues and Gustavo M. Dalpian},
url = {https://arxiv.org/abs/2306.16496},
doi = {10.48550/arXiv.2306.16496},
year = {2023},
date = {2023-01-01},
urldate = {2023-01-01},
abstract = {With the availability of extensive databases of inorganic materials, data-driven approaches leveraging machine learning have gained prominence in materials science research. In this study, we propose an innovative adaptation of data-driven concepts to the mapping and exploration of chemical compound space. Recommender systems, widely utilized for suggesting items to users, employ techniques such as collaborative filtering, which rely on bipartite graphs composed of users, items, and their interactions. Building upon the Open Quantum Materials Database (OQMD), we constructed a bipartite graph where elements from the periodic table and sites within crystal structures are treated as separate entities. The relationships between them, defined by the presence of ions at specific sites and weighted according to the thermodynamic stability of the respective compounds, allowed us to generate an embedding space that contains vector representations for each ion and each site. Through the correlation of ion-site occupancy with their respective distances within the embedding space, we explored new ion-site occupancies, facilitating the discovery of novel stable compounds. Moreover, the graph's embedding space enabled a comprehensive examination of chemical similarities among elements, and a detailed analysis of local geometries of sites. To demonstrate the effectiveness and robustness of our method, we conducted a historical evaluation using different versions of the OQMD and recommended new compounds with Kagome lattices, showcasing the applicability of our approach to practical materials design.},
keywords = {},
pubstate = {published},
tppubtype = {workingpaper}
}
With the availability of extensive databases of inorganic materials, data-driven approaches leveraging machine learning have gained prominence in materials science research. In this study, we propose an innovative adaptation of data-driven concepts to the mapping and exploration of chemical compound space. Recommender systems, widely utilized for suggesting items to users, employ techniques such as collaborative filtering, which rely on bipartite graphs composed of users, items, and their interactions. Building upon the Open Quantum Materials Database (OQMD), we constructed a bipartite graph where elements from the periodic table and sites within crystal structures are treated as separate entities. The relationships between them, defined by the presence of ions at specific sites and weighted according to the thermodynamic stability of the respective compounds, allowed us to generate an embedding space that contains vector representations for each ion and each site. Through the correlation of ion-site occupancy with their respective distances within the embedding space, we explored new ion-site occupancies, facilitating the discovery of novel stable compounds. Moreover, the graph's embedding space enabled a comprehensive examination of chemical similarities among elements, and a detailed analysis of local geometries of sites. To demonstrate the effectiveness and robustness of our method, we conducted a historical evaluation using different versions of the OQMD and recommended new compounds with Kagome lattices, showcasing the applicability of our approach to practical materials design.
Bezzon, Vinícius Danilo Nonato; Caturello, Naidel Antonio Moreira Santos; Dalpian, Gustavo M.; Ferreira, Fabio Furlan
Crystal structure determination and DFT analysis of doxorubicin hydrochloride for controlled-release drug formulations Journal Article
Em: Journal of Molecular Structure, vol. 1294, pp. 136412, 2023, ISSN: 0022-2860.
@article{BEZZON2023136412,
title = {Crystal structure determination and DFT analysis of doxorubicin hydrochloride for controlled-release drug formulations},
author = {Vinícius Danilo Nonato Bezzon and Naidel Antonio Moreira Santos Caturello and Gustavo M. Dalpian and Fabio Furlan Ferreira},
url = {https://www.sciencedirect.com/science/article/pii/S0022286023015028},
doi = {https://doi.org/10.1016/j.molstruc.2023.136412},
issn = {0022-2860},
year = {2023},
date = {2023-01-01},
urldate = {2023-01-01},
journal = {Journal of Molecular Structure},
volume = {1294},
pages = {136412},
abstract = {Doxorubicin hydrochloride (DOX) is a widely used chemotherapeutic drug that inhibits the growth of cancer cells. Many DOX-based controlled-release systems have been proposed to reduce toxicity. However, knowledge of its crystal structure is essential for optimizing drug release processes and designing co-crystals or salts with different release properties. Although DOX has been extensively studied, no crystal structure is available in the Cambridge Structural Database or literature. In this work, we determine the crystal structure of DOX using a simulated annealing approach based on powder X-ray diffraction data. We confirm its validation by Rietveld refinement and molecular cohesion by using a molecular geometry check tool. We also use density functional theory to optimize the DOX structure and obtain the minimum energy conformation, H-bond donor/acceptor species, charge localization, and crystal structure parameters. This study provides essential structural information on DOX that can be used to rationalize new modified-release dosage forms and to design co-crystals or salts with different release properties.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Doxorubicin hydrochloride (DOX) is a widely used chemotherapeutic drug that inhibits the growth of cancer cells. Many DOX-based controlled-release systems have been proposed to reduce toxicity. However, knowledge of its crystal structure is essential for optimizing drug release processes and designing co-crystals or salts with different release properties. Although DOX has been extensively studied, no crystal structure is available in the Cambridge Structural Database or literature. In this work, we determine the crystal structure of DOX using a simulated annealing approach based on powder X-ray diffraction data. We confirm its validation by Rietveld refinement and molecular cohesion by using a molecular geometry check tool. We also use density functional theory to optimize the DOX structure and obtain the minimum energy conformation, H-bond donor/acceptor species, charge localization, and crystal structure parameters. This study provides essential structural information on DOX that can be used to rationalize new modified-release dosage forms and to design co-crystals or salts with different release properties.
Yadav, Asha; Acosta, Carlos Mera; Dalpian, Gustavo M.; Malyi, Oleksandr I.
First-principles investigations of 2D materials: Challenges and best practices Journal Article
Em: Matter, vol. 6, não 9, pp. 2711-2734, 2023, ISSN: 2590-2385.
@article{YADAV20232711,
title = {First-principles investigations of 2D materials: Challenges and best practices},
author = {Asha Yadav and Carlos Mera Acosta and Gustavo M. Dalpian and Oleksandr I. Malyi},
url = {https://www.sciencedirect.com/science/article/pii/S2590238523002370},
doi = {https://doi.org/10.1016/j.matt.2023.05.019},
issn = {2590-2385},
year = {2023},
date = {2023-01-01},
journal = {Matter},
volume = {6},
number = {9},
pages = {2711-2734},
abstract = {Summary
The successful exfoliation of graphene from graphite has brought significant attention to predicting new two-dimensional (2D) materials that can be realized experimentally. As a consequence, first-principles studies of novel 2D materials become routine, with thousands of papers published every year. What makes these studies interesting is that they predict new materials that have not been realized yet but should be a panacea for topological insulators, next-generation battery electrodes, novel solar cell absorbers, etc. There is no doubt that some of the proposed materials can provide a specific solution, and their properties/performance can be confirmed experimentally. At the same time, there are many false predictions because of the computational errors or the Legoland approach used to study 2D materials. To reduce the gap between theoretical and experimental works, we performed a systematic review of computational and Legoland factors that should be minimized in future theoretical works.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Summary
The successful exfoliation of graphene from graphite has brought significant attention to predicting new two-dimensional (2D) materials that can be realized experimentally. As a consequence, first-principles studies of novel 2D materials become routine, with thousands of papers published every year. What makes these studies interesting is that they predict new materials that have not been realized yet but should be a panacea for topological insulators, next-generation battery electrodes, novel solar cell absorbers, etc. There is no doubt that some of the proposed materials can provide a specific solution, and their properties/performance can be confirmed experimentally. At the same time, there are many false predictions because of the computational errors or the Legoland approach used to study 2D materials. To reduce the gap between theoretical and experimental works, we performed a systematic review of computational and Legoland factors that should be minimized in future theoretical works.
The successful exfoliation of graphene from graphite has brought significant attention to predicting new two-dimensional (2D) materials that can be realized experimentally. As a consequence, first-principles studies of novel 2D materials become routine, with thousands of papers published every year. What makes these studies interesting is that they predict new materials that have not been realized yet but should be a panacea for topological insulators, next-generation battery electrodes, novel solar cell absorbers, etc. There is no doubt that some of the proposed materials can provide a specific solution, and their properties/performance can be confirmed experimentally. At the same time, there are many false predictions because of the computational errors or the Legoland approach used to study 2D materials. To reduce the gap between theoretical and experimental works, we performed a systematic review of computational and Legoland factors that should be minimized in future theoretical works.
Ussui, Valter; Lazar, Dolores Ribeiro; Lima, Nelson; Arata, Anelyse; Ribeiro, Fabio; Dalpian, Gustavo M.; Marchi, Juliana; Paschoal, José Octavio
Room temperature plasticity of zirconia-yttria-titania ceramics: Experimental indications and structural modelling Journal Article
Em: PAC, vol. 16, não 4, pp. 367–373, 2023, ISSN: 2406-1034.
@article{Ussui2022,
title = {Room temperature plasticity of zirconia-yttria-titania ceramics: Experimental indications and structural modelling},
author = {Valter Ussui and Dolores Ribeiro Lazar and Nelson Lima and Anelyse Arata and Fabio Ribeiro and Gustavo M. Dalpian and Juliana Marchi and José Octavio Paschoal},
doi = {10.2298/pac2204367u},
issn = {2406-1034},
year = {2023},
date = {2023-01-01},
journal = {PAC},
volume = {16},
number = {4},
pages = {367–373},
publisher = {National Library of Serbia},
abstract = {<jats:p>Yttria-stabilized tetragonal zirconia (Y-TZP) ceramics have excellent
mechanical properties. However, such materials cannot undergo plastic
deformation at room temperature due to their high hardness and brittleness
values, hindering machinability. To overcome these limitations, we propose a
zirconia-yttria-titania ceramics, based on zirconia containing 3mol% yttria
and up to 15mol% titania. The zirconia-yttria-titania powders were
synthesized by co-precipitation method, uniaxially pressed and sintered at
1400?C/5 h. Sample characterizations were carried out by X-ray diffraction,
scanning electron microscopy and mechanical properties through Vickers
hardness and toughness measurements. Compared to the Y-TZP ceramics, the
yttria stabilised tetragonal zirconia ceramics co-doped with 10mol%Ti showed
noticeable increase of tetragonality parameter, higher toughness and lower
hardness values, indicating plasticity at room temperature. Furthermore, the
atomistic simulation by Density Functional Theory methodology suggests the
occurrence of spatial arrangement of the atoms, explaining the proposed
plasticity.</jats:p>},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
<jats:p>Yttria-stabilized tetragonal zirconia (Y-TZP) ceramics have excellent
mechanical properties. However, such materials cannot undergo plastic
deformation at room temperature due to their high hardness and brittleness
values, hindering machinability. To overcome these limitations, we propose a
zirconia-yttria-titania ceramics, based on zirconia containing 3mol% yttria
and up to 15mol% titania. The zirconia-yttria-titania powders were
synthesized by co-precipitation method, uniaxially pressed and sintered at
1400?C/5 h. Sample characterizations were carried out by X-ray diffraction,
scanning electron microscopy and mechanical properties through Vickers
hardness and toughness measurements. Compared to the Y-TZP ceramics, the
yttria stabilised tetragonal zirconia ceramics co-doped with 10mol%Ti showed
noticeable increase of tetragonality parameter, higher toughness and lower
hardness values, indicating plasticity at room temperature. Furthermore, the
atomistic simulation by Density Functional Theory methodology suggests the
occurrence of spatial arrangement of the atoms, explaining the proposed
plasticity.</jats:p>
mechanical properties. However, such materials cannot undergo plastic
deformation at room temperature due to their high hardness and brittleness
values, hindering machinability. To overcome these limitations, we propose a
zirconia-yttria-titania ceramics, based on zirconia containing 3mol% yttria
and up to 15mol% titania. The zirconia-yttria-titania powders were
synthesized by co-precipitation method, uniaxially pressed and sintered at
1400?C/5 h. Sample characterizations were carried out by X-ray diffraction,
scanning electron microscopy and mechanical properties through Vickers
hardness and toughness measurements. Compared to the Y-TZP ceramics, the
yttria stabilised tetragonal zirconia ceramics co-doped with 10mol%Ti showed
noticeable increase of tetragonality parameter, higher toughness and lower
hardness values, indicating plasticity at room temperature. Furthermore, the
atomistic simulation by Density Functional Theory methodology suggests the
occurrence of spatial arrangement of the atoms, explaining the proposed
plasticity.</jats:p>
