Comitê Gestor
IFT-UNESP
Alexandre Reily Rocha
Publicações
2026
Amorim, Felippe; Santos, Washington F.; Ferreira, Mauro S.; Rocha, Alexandre Reily; Lewenkopf, Caio
Anomalous Localization in Magnetically Doped Two-Dimensional Topological Insulators Miscellaneous
2026.
@misc{amorim2026anomalouslocalizationmagneticallydoped,
title = {Anomalous Localization in Magnetically Doped Two-Dimensional Topological Insulators},
author = {Felippe Amorim and Washington F. Santos and Mauro S. Ferreira and Alexandre Reily Rocha and Caio Lewenkopf},
url = {https://arxiv.org/abs/2607.24373},
year = {2026},
date = {2026-07-27},
urldate = {2026-01-01},
abstract = {Two-dimensional topological insulators (2DTIs) harbor spin-polarized edge states that are topologically protected by time-reversal symmetry against non-magnetic structural disorder. However, coupling to magnetic impurities breaks this symmetry, inducing backscattering and destroying perfect quantization. While the impact of isolated dilute magnetic impurities is well understood, the transport properties in the presence of dense, disordered ensembles of magnetic moments remain poorly understood. In this work, we develop an analytical framework, supported by extensive numerical simulations, that captures the behavior of edge transport in two-dimensional topological insulators (2DTIs) with a finite concentration of magnetic impurities. We predict the onset of Anderson localization and uncover an anomalous localization regime characterized by a sub-exponential decay of the conductance, scaling as lnG∝−L−−√, where L is the system length. Furthermore, we demonstrate that the transport exhibits a universal scaling behavior governed solely by the effective impurity concentration. Applying our model to Mn-doped HgTe quantum wells, we find excellent agreement with experimental data. These findings provide a theoretical foundation for understanding anomalous localization phenomena in magnetically doped topological phases.},
keywords = {},
pubstate = {published},
tppubtype = {misc}
}
Two-dimensional topological insulators (2DTIs) harbor spin-polarized edge states that are topologically protected by time-reversal symmetry against non-magnetic structural disorder. However, coupling to magnetic impurities breaks this symmetry, inducing backscattering and destroying perfect quantization. While the impact of isolated dilute magnetic impurities is well understood, the transport properties in the presence of dense, disordered ensembles of magnetic moments remain poorly understood. In this work, we develop an analytical framework, supported by extensive numerical simulations, that captures the behavior of edge transport in two-dimensional topological insulators (2DTIs) with a finite concentration of magnetic impurities. We predict the onset of Anderson localization and uncover an anomalous localization regime characterized by a sub-exponential decay of the conductance, scaling as lnG∝−L−−√, where L is the system length. Furthermore, we demonstrate that the transport exhibits a universal scaling behavior governed solely by the effective impurity concentration. Applying our model to Mn-doped HgTe quantum wells, we find excellent agreement with experimental data. These findings provide a theoretical foundation for understanding anomalous localization phenomena in magnetically doped topological phases.
Venezuela, Pedro; Marinho, Enesio; Rocha, Alexandre Reily; Villegas, Cesar E. P.
Layer-Dependent Optical Properties of Orthorhombic B _2 N _2 : Prospects for Photovoltaics Journal Article
Em: ACS Appl. Energy Mater., 2026, ISSN: 2574-0962.
@article{Venezuela2026,
title = {Layer-Dependent Optical Properties of Orthorhombic B _2 N _2 : Prospects for Photovoltaics},
author = {Pedro Venezuela and Enesio Marinho and Alexandre Reily Rocha and Cesar E. P. Villegas},
doi = {10.1021/acsaem.6c00153},
issn = {2574-0962},
year = {2026},
date = {2026-04-16},
urldate = {2026-04-16},
journal = {ACS Appl. Energy Mater.},
publisher = {American Chemical Society (ACS)},
abstract = {Fundamental understanding of exciton formation is of utmost importance for a wide variety of optoelectronic applications, as this elementary quasiparticle strongly influences the absorption, charge separation, and photocurrent generation processes. While hexagonal boron nitride stands out for its high thermal stability and chemical inertness, its wide band gap hampers its use in several optoelectronic applications, including photovoltaics. Here, by employing ab initio many-body excited-state methods, we elucidate how the electronic and optical properties of orthorhombic B2N2 evolve with layer thickness, from the three-dimensional bulk to intermediate multilayers and down to the monolayer limit. The results indicate that the quasiparticle gap can be tuned from 2.41 eV, for the monolayer, down to 1.28 eV in the bulk limit. Interestingly, the studied excitonic response exhibits prominent peaks in the near-infrared range, going from 1.4 to 1.7 eV, which highlights their potential as an active sunlight absorber material. Finally, we model a prototypical single-junction solar cell based on bulk B2N2, finding that a 150-nm-thick active layer achieves power conversion efficiencies between 16.8% and 24.9% in the nonradiative and radiative limits, respectively. Our calculations suggest the potential of B2N2-based thin films for the design of flexible solar cells.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Fundamental understanding of exciton formation is of utmost importance for a wide variety of optoelectronic applications, as this elementary quasiparticle strongly influences the absorption, charge separation, and photocurrent generation processes. While hexagonal boron nitride stands out for its high thermal stability and chemical inertness, its wide band gap hampers its use in several optoelectronic applications, including photovoltaics. Here, by employing ab initio many-body excited-state methods, we elucidate how the electronic and optical properties of orthorhombic B2N2 evolve with layer thickness, from the three-dimensional bulk to intermediate multilayers and down to the monolayer limit. The results indicate that the quasiparticle gap can be tuned from 2.41 eV, for the monolayer, down to 1.28 eV in the bulk limit. Interestingly, the studied excitonic response exhibits prominent peaks in the near-infrared range, going from 1.4 to 1.7 eV, which highlights their potential as an active sunlight absorber material. Finally, we model a prototypical single-junction solar cell based on bulk B2N2, finding that a 150-nm-thick active layer achieves power conversion efficiencies between 16.8% and 24.9% in the nonradiative and radiative limits, respectively. Our calculations suggest the potential of B2N2-based thin films for the design of flexible solar cells.
Venezuela, Pedro; Marinho, Enesio; Rocha, Alexandre Reily; Villegas, Cesar E. P.
Layer-Dependent Optical Properties of Orthorhombic B _2 N _2 : Prospects for Photovoltaics Journal Article
Em: ACS Appl. Energy Mater., 2026, ISSN: 2574-0962.
@article{Venezuela2026b,
title = {Layer-Dependent Optical Properties of Orthorhombic B _2 N _2 : Prospects for Photovoltaics},
author = {Pedro Venezuela and Enesio Marinho and Alexandre Reily Rocha and Cesar E. P. Villegas},
doi = {10.1021/acsaem.6c00153},
issn = {2574-0962},
year = {2026},
date = {2026-04-16},
urldate = {2026-04-16},
journal = {ACS Appl. Energy Mater.},
publisher = {American Chemical Society (ACS)},
abstract = {Fundamental understanding of exciton formation is of utmost importance for a wide variety of optoelectronic applications, as this elementary quasiparticle strongly influences the absorption, charge separation, and photocurrent generation processes. While hexagonal boron nitride stands out for its high thermal stability and chemical inertness, its wide band gap hampers its use in several optoelectronic applications, including photovoltaics. Here, by employing ab initio many-body excited-state methods, we elucidate how the electronic and optical properties of orthorhombic B2N2 evolve with layer thickness, from the three-dimensional bulk to intermediate multilayers and down to the monolayer limit. The results indicate that the quasiparticle gap can be tuned from 2.41 eV, for the monolayer, down to 1.28 eV in the bulk limit. Interestingly, the studied excitonic response exhibits prominent peaks in the near-infrared range, going from 1.4 to 1.7 eV, which highlights their potential as an active sunlight absorber material. Finally, we model a prototypical single-junction solar cell based on bulk B2N2, finding that a 150-nm-thick active layer achieves power conversion efficiencies between 16.8% and 24.9% in the nonradiative and radiative limits, respectively. Our calculations suggest the potential of B2N2-based thin films for the design of flexible solar cells.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Fundamental understanding of exciton formation is of utmost importance for a wide variety of optoelectronic applications, as this elementary quasiparticle strongly influences the absorption, charge separation, and photocurrent generation processes. While hexagonal boron nitride stands out for its high thermal stability and chemical inertness, its wide band gap hampers its use in several optoelectronic applications, including photovoltaics. Here, by employing ab initio many-body excited-state methods, we elucidate how the electronic and optical properties of orthorhombic B2N2 evolve with layer thickness, from the three-dimensional bulk to intermediate multilayers and down to the monolayer limit. The results indicate that the quasiparticle gap can be tuned from 2.41 eV, for the monolayer, down to 1.28 eV in the bulk limit. Interestingly, the studied excitonic response exhibits prominent peaks in the near-infrared range, going from 1.4 to 1.7 eV, which highlights their potential as an active sunlight absorber material. Finally, we model a prototypical single-junction solar cell based on bulk B2N2, finding that a 150-nm-thick active layer achieves power conversion efficiencies between 16.8% and 24.9% in the nonradiative and radiative limits, respectively. Our calculations suggest the potential of B2N2-based thin films for the design of flexible solar cells.
Lizárraga, K.; Villegas, Cesar E. P.; Lira, R.; Serquen, E.; Liu, Hsiang-Lin; Guerra, J. A.; Rocha, A. R.; Venezuela, P.
Dispersion model for the optical absorption of two-dimensional materials Journal Article
Em: Phys. Rev. B, vol. 113, não 4, 2026, ISSN: 2469-9969.
@article{Lizárraga2026,
title = {Dispersion model for the optical absorption of two-dimensional materials},
author = {K. Lizárraga and Cesar E. P. Villegas and R. Lira and E. Serquen and Hsiang-Lin Liu and J. A. Guerra and A. R. Rocha and P. Venezuela},
doi = {10.1103/2mhl-4vgh},
issn = {2469-9969},
year = {2026},
date = {2026-01-07},
journal = {Phys. Rev. B},
volume = {113},
number = {4},
publisher = {American Physical Society (APS)},
abstract = {The optical response of two-dimensional systems is strongly influenced by tightly bound excitons. Despite its relevance in helping predict device performance, the current derivation of the two-dimensional Elliott equation is rarely used to estimate exciton binding energy and band gap in these systems, primarily due to its lack of an analytical form and the complexity introduced by substrate interactions. In this work, we present a new approach based on optical absorption measurements via an extended Elliott band fluctuations model, which notably provides analytical expressions for isotropic systems. Our method accurately captures the optical absorption near the band edge, fully incorporating spin–orbit band splitting and substrate effects via the Keldysh effective potential. It also includes the influence of surface and interface contributions to the dielectric environment, which give rise to localized defect-related absorption features. We apply this approach to key transition metal dichalcogenides (MoS2, MoSe2, WS2, and WSe2) exhibiting small and large spin-orbit band splitting, on various substrates and over a broad temperature range. The results show good agreement with magnetoabsorption and photoluminescence measurements, allowing for an accurate description of excitonic properties using only optical measurements and is readily extendable to other 2D isotropic materials.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The optical response of two-dimensional systems is strongly influenced by tightly bound excitons. Despite its relevance in helping predict device performance, the current derivation of the two-dimensional Elliott equation is rarely used to estimate exciton binding energy and band gap in these systems, primarily due to its lack of an analytical form and the complexity introduced by substrate interactions. In this work, we present a new approach based on optical absorption measurements via an extended Elliott band fluctuations model, which notably provides analytical expressions for isotropic systems. Our method accurately captures the optical absorption near the band edge, fully incorporating spin–orbit band splitting and substrate effects via the Keldysh effective potential. It also includes the influence of surface and interface contributions to the dielectric environment, which give rise to localized defect-related absorption features. We apply this approach to key transition metal dichalcogenides (MoS2, MoSe2, WS2, and WSe2) exhibiting small and large spin-orbit band splitting, on various substrates and over a broad temperature range. The results show good agreement with magnetoabsorption and photoluminescence measurements, allowing for an accurate description of excitonic properties using only optical measurements and is readily extendable to other 2D isotropic materials.
Squillante, Lucas; Soares, Samuel M.; Jr., E. Marinho; Rocha, Alexandre R.; Figueira, M. S.; Seridonio, Antonio C.; Souza, Mariano
Uma introdução compreensiva sobre fenômenos eletrônicos fortemente correlacionados Journal Article
Em: Rev. Bras. Ensino Fís., vol. 48, 2026, ISSN: 1806-9126.
@article{Squillante2026,
title = {Uma introdução compreensiva sobre fenômenos eletrônicos fortemente correlacionados},
author = {Lucas Squillante and Samuel M. Soares and E. Marinho Jr. and Alexandre R. Rocha and M. S. Figueira and Antonio C. Seridonio and Mariano Souza},
doi = {10.1590/1806-9126-rbef-2025-0547},
issn = {1806-9126},
year = {2026},
date = {2026-01-01},
journal = {Rev. Bras. Ensino Fís.},
volume = {48},
publisher = {FapUNIFESP (SciELO)},
abstract = {<jats:p>Resumo O modelo do gás de elétrons proposto por Fermi em 1926 constitui uma das primeiras aplicações diretas da Mecânica Quântica na descrição das propriedades físicas de sólidos. Em particular, a descrição matemática da contribuição eletrônica para o calor específico consiste em um elemento central neste campo. No entanto, manifestações exóticas da matéria não podem ser descritas pelo modelo do gás de Fermi e pela teoria de bandas. Exemplos incluem a fase isolante de Mott e o alto valor do coeficiente de Sommerfeld para os chamados férmions pesados. Nesta contribuição, revisitamos de forma compreensiva os conceitos fundamentais relacionados aos fenômenos eletrônicos fortemente correlacionados. Focamos em uma análise do modelo de Hubbard para o dímero de Mott em conexão direta com tópicos atuais de pesquisa e observações experimentais. Revisitamos também brevemente os modelos de Fermi-Hubbard, Bose-Fermi-Hubbard, Anderson de uma única impureza, Su–Schrieffer–Heeger, t- J e RVB, bem como a teoria BCS e a do funcional da densidade e suas aplicações. Ainda, a teoria de campo médio dinâmico e a aproximação GW são brevemente discutidas. O presente trabalho pode ser visto como uma “cartilha” para o público geral interessado nos aspectos teóricos e experimentais relacionados à pesquisa no campo de sistemas eletrônicos fortemente correlacionados.</jats:p>},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
<jats:p>Resumo O modelo do gás de elétrons proposto por Fermi em 1926 constitui uma das primeiras aplicações diretas da Mecânica Quântica na descrição das propriedades físicas de sólidos. Em particular, a descrição matemática da contribuição eletrônica para o calor específico consiste em um elemento central neste campo. No entanto, manifestações exóticas da matéria não podem ser descritas pelo modelo do gás de Fermi e pela teoria de bandas. Exemplos incluem a fase isolante de Mott e o alto valor do coeficiente de Sommerfeld para os chamados férmions pesados. Nesta contribuição, revisitamos de forma compreensiva os conceitos fundamentais relacionados aos fenômenos eletrônicos fortemente correlacionados. Focamos em uma análise do modelo de Hubbard para o dímero de Mott em conexão direta com tópicos atuais de pesquisa e observações experimentais. Revisitamos também brevemente os modelos de Fermi-Hubbard, Bose-Fermi-Hubbard, Anderson de uma única impureza, Su–Schrieffer–Heeger, t- J e RVB, bem como a teoria BCS e a do funcional da densidade e suas aplicações. Ainda, a teoria de campo médio dinâmico e a aproximação GW são brevemente discutidas. O presente trabalho pode ser visto como uma “cartilha” para o público geral interessado nos aspectos teóricos e experimentais relacionados à pesquisa no campo de sistemas eletrônicos fortemente correlacionados.</jats:p>
2025
Torres, Alberto; Oliveira, Alan Barros; Barbosa, Mathus Santos; Lelovsky, Leonardo Villegas; Resende, Valdirene; Dutra, Flávio; Pimenta, Felipe; Parreira, Fabricio; Souza, Amaury Mello; Matos, Matheus Josué Souza; Rocha, Alexandre Reily
Machine learning interatomic potential for the structural properties iron oxides Não publicado
Research Square, 2025.
@unpublished{Torres2025,
title = {Machine learning interatomic potential for the structural properties iron oxides},
author = {Alberto Torres and Alan Barros Oliveira and Mathus Santos Barbosa and Leonardo Villegas Lelovsky and Valdirene Resende and Flávio Dutra and Felipe Pimenta and Fabricio Parreira and Amaury Mello Souza and Matheus Josué Souza Matos and Alexandre Reily Rocha},
url = {https://www.researchsquare.com/article/rs-8031034/v1},
doi = {10.21203/rs.3.rs-8031034/v1},
year = {2025},
date = {2025-11-25},
urldate = {2025-11-25},
publisher = {Springer Science and Business Media LLC},
abstract = {<title>Abstract</title>
<p>Iron oxides constitute an important class of materials, exhibiting a rich and intricate range of behaviors. Despite their significance, the structural and mechanical properties, particularly of Hematite ($alpha$-Fe2O3), have been scarcely investigated in the literature. At the same time, recent developments in machine learning for interatomic potentials have revolutionized computational materials science by enabling highly accurate and efficient simulations of atomic interactions. Traditional methods, such as density functional theory (DFT) and classical force fields, often struggle with high computational costs or lack the flexibility to generalize across diverse chemical environments. ML-based approaches have emerged as powerful alternatives, learning complex potential energy surfaces from quantum-mechanical data. These models can achieve DFT accuracy at a fraction of the computational cost, facilitating large-scale molecular dynamics (MD) simulations.
In this work, we present a graph neural network interatomic potential for hematite. The model was trained on datasets generated from DFT+U calculations to account for strong electronic correlations, using atomic configurations sampled across a wide range of temperatures and pressures. Our potential accurately reproduces fundamental material properties, including the elastic moduli, anisotropic elastic constants, vibrational frequencies, and surface energies. Furthermore, we demonstrate its transferability to other bulk iron oxides. This work enables large-scale molecular dynamics (MD) simulations of iron-based materials with ab initio accuracy at a computational cost comparable to that of classical potentials, opening new opportunities for investigating these complex systems.</p>},
howpublished = {Research Square},
keywords = {},
pubstate = {published},
tppubtype = {unpublished}
}
<title>Abstract</title>
<p>Iron oxides constitute an important class of materials, exhibiting a rich and intricate range of behaviors. Despite their significance, the structural and mechanical properties, particularly of Hematite ($alpha$-Fe2O3), have been scarcely investigated in the literature. At the same time, recent developments in machine learning for interatomic potentials have revolutionized computational materials science by enabling highly accurate and efficient simulations of atomic interactions. Traditional methods, such as density functional theory (DFT) and classical force fields, often struggle with high computational costs or lack the flexibility to generalize across diverse chemical environments. ML-based approaches have emerged as powerful alternatives, learning complex potential energy surfaces from quantum-mechanical data. These models can achieve DFT accuracy at a fraction of the computational cost, facilitating large-scale molecular dynamics (MD) simulations.
In this work, we present a graph neural network interatomic potential for hematite. The model was trained on datasets generated from DFT+U calculations to account for strong electronic correlations, using atomic configurations sampled across a wide range of temperatures and pressures. Our potential accurately reproduces fundamental material properties, including the elastic moduli, anisotropic elastic constants, vibrational frequencies, and surface energies. Furthermore, we demonstrate its transferability to other bulk iron oxides. This work enables large-scale molecular dynamics (MD) simulations of iron-based materials with ab initio accuracy at a computational cost comparable to that of classical potentials, opening new opportunities for investigating these complex systems.</p>
<p>Iron oxides constitute an important class of materials, exhibiting a rich and intricate range of behaviors. Despite their significance, the structural and mechanical properties, particularly of Hematite ($alpha$-Fe2O3), have been scarcely investigated in the literature. At the same time, recent developments in machine learning for interatomic potentials have revolutionized computational materials science by enabling highly accurate and efficient simulations of atomic interactions. Traditional methods, such as density functional theory (DFT) and classical force fields, often struggle with high computational costs or lack the flexibility to generalize across diverse chemical environments. ML-based approaches have emerged as powerful alternatives, learning complex potential energy surfaces from quantum-mechanical data. These models can achieve DFT accuracy at a fraction of the computational cost, facilitating large-scale molecular dynamics (MD) simulations.
In this work, we present a graph neural network interatomic potential for hematite. The model was trained on datasets generated from DFT+U calculations to account for strong electronic correlations, using atomic configurations sampled across a wide range of temperatures and pressures. Our potential accurately reproduces fundamental material properties, including the elastic moduli, anisotropic elastic constants, vibrational frequencies, and surface energies. Furthermore, we demonstrate its transferability to other bulk iron oxides. This work enables large-scale molecular dynamics (MD) simulations of iron-based materials with ab initio accuracy at a computational cost comparable to that of classical potentials, opening new opportunities for investigating these complex systems.</p>
Rocha, Alexandre R.; Amorim, Rodrigo G.; Scopel, Wanderlã L.; Villegas, Cesar E. P.
Tunable Interlayer Excitons in Bilayer Graphene Nanoribbons Miscellaneous
2025.
@misc{rocha2025tunableinterlayerexcitonsbilayer,
title = {Tunable Interlayer Excitons in Bilayer Graphene Nanoribbons},
author = {Alexandre R. Rocha and Rodrigo G. Amorim and Wanderlã L. Scopel and Cesar E. P. Villegas},
url = {https://arxiv.org/abs/2507.10887},
year = {2025},
date = {2025-07-15},
urldate = {2025-01-01},
abstract = {Vertically stacked van der Waals structures are promising platforms that enable layer engineering, opening new avenues for the quantum control of elementary excitations, including optically generated bound electron-hole pairs. Here we employ excited-state density functional calculations to demonstrate strong interlayer excitonic coupling in one-dimensional van der Waals nanostructures derived from armchair graphene nanoribbons. The excitonic response exhibits prominent peaks in the near-infrared range, mainly attributed to intralayer excitons, while interlayer excitations with absorption peak strengths of up to 13% of the maximum absorption are also observed. Both type-I and type-II band alignments are found, which promote the formation of intralayer and interlayer excitons. Notably, interlayer excitons in these systems exhibit long-lived radiative lifetimes at room temperature, ranging from 1 nanosecond to 9.4 microseconds. Our calculations suggest the potential to tune the excitonic response and lifetimes of bilayer graphene nanoribbons via careful engineering of the stacking order.},
keywords = {},
pubstate = {published},
tppubtype = {misc}
}
Vertically stacked van der Waals structures are promising platforms that enable layer engineering, opening new avenues for the quantum control of elementary excitations, including optically generated bound electron-hole pairs. Here we employ excited-state density functional calculations to demonstrate strong interlayer excitonic coupling in one-dimensional van der Waals nanostructures derived from armchair graphene nanoribbons. The excitonic response exhibits prominent peaks in the near-infrared range, mainly attributed to intralayer excitons, while interlayer excitations with absorption peak strengths of up to 13% of the maximum absorption are also observed. Both type-I and type-II band alignments are found, which promote the formation of intralayer and interlayer excitons. Notably, interlayer excitons in these systems exhibit long-lived radiative lifetimes at room temperature, ranging from 1 nanosecond to 9.4 microseconds. Our calculations suggest the potential to tune the excitonic response and lifetimes of bilayer graphene nanoribbons via careful engineering of the stacking order.
Mannino, Anthony; Arvelos, Graciele M.; Kaushik, Kedarsh; Artacho, Emilio; Ordejon, Pablo; Rocha, Alexandre R.; Pedroza, Luana S.; Fernández-Serra, Marivi
First-Principles Nanocapacitor Simulations of the Optical Dielectric Constant in Water Ice Miscellaneous
2025.
@misc{mannino2025firstprinciplesnanocapacitorsimulationsoptical,
title = {First-Principles Nanocapacitor Simulations of the Optical Dielectric Constant in Water Ice},
author = {Anthony Mannino and Graciele M. Arvelos and Kedarsh Kaushik and Emilio Artacho and Pablo Ordejon and Alexandre R. Rocha and Luana S. Pedroza and Marivi Fernández-Serra},
url = {https://arxiv.org/abs/2506.23003},
year = {2025},
date = {2025-06-28},
urldate = {2025-01-01},
abstract = {We introduce a combined density functional theory (DFT) and non-equilibrium Green's function (NEGF) framework to compute the capacitance of nanocapacitors and directly extract the dielectric response of a sub-nanometer dielectric under bias. We identify that at the nanoscale conventional capacitance evaluations based on stored charge per unit voltage suffer from an ill-posed partitioning of electrode and dielectric charge. This partitioning directly impacts the geometric definition of capacitance through the capacitor width, which in turn makes the evaluation of dielectric response uncertain. This ambiguous separation further induces spurious interfacial polarizability when analyzed via maximally localized Wannier functions. Focusing on crystalline ice, we develop a robust charge-separation protocol that yields unique capacitance-derived polarizability and dielectric constants, unequivocally demonstrating that confinement neither alters ice's intrinsic electronic response nor its insensitivity to proton order. Our results lay the groundwork for rigorous interpretation of capacitor measurements in low-dimensional dielectric materials.},
keywords = {},
pubstate = {published},
tppubtype = {misc}
}
We introduce a combined density functional theory (DFT) and non-equilibrium Green's function (NEGF) framework to compute the capacitance of nanocapacitors and directly extract the dielectric response of a sub-nanometer dielectric under bias. We identify that at the nanoscale conventional capacitance evaluations based on stored charge per unit voltage suffer from an ill-posed partitioning of electrode and dielectric charge. This partitioning directly impacts the geometric definition of capacitance through the capacitor width, which in turn makes the evaluation of dielectric response uncertain. This ambiguous separation further induces spurious interfacial polarizability when analyzed via maximally localized Wannier functions. Focusing on crystalline ice, we develop a robust charge-separation protocol that yields unique capacitance-derived polarizability and dielectric constants, unequivocally demonstrating that confinement neither alters ice's intrinsic electronic response nor its insensitivity to proton order. Our results lay the groundwork for rigorous interpretation of capacitor measurements in low-dimensional dielectric materials.
Lizárraga, K.; Guerra, J. A.; Enrique-Moran, L. A.; Serquen, E.; Ventura, E.; Villegas, Cesar E. P.; Rocha, A. R.; Venezuela, P.
2025.
@misc{lizárraga2025determiningexcitonbindingenergy,
title = {Determining Exciton Binding Energy and Reduced Effective Mass in Metal Tri-Halide Perovskites from Optical and Impedance Spectroscopy Measurements},
author = {K. Lizárraga and J. A. Guerra and L. A. Enrique-Moran and E. Serquen and E. Ventura and Cesar E. P. Villegas and A. R. Rocha and P. Venezuela},
url = {https://arxiv.org/abs/2506.22680},
year = {2025},
date = {2025-06-27},
urldate = {2025-06-27},
abstract = {Accurate determination of the exciton binding energy and reduced effective mass in halide perovskites is of utmost importance for the selective design of optoelectronic devices. Although these properties are currently determined by several spectroscopic techniques, complementary theoretical models are often required to bridge macroscopic and microscopic properties. Here, we present a novel method to determine these quantities while fully accounting for polarization effects due to carrier interactions with longitudinal optical phonons. Our approach estimates the exciton-polaron binding energy from optical absorption measurements using a recently developed Elliott based Band Fluctuations model. The reduced effective mass is obtained via the Pollmann-Buttner exciton-polaron model, which is based on the Frohlich polaron framework, where the strength of the electron-phonon interaction arises from changes in the dielectric properties. The procedure is applied to the family of perovskites ABX3 (A = MA, FA, Cs; B = Pb; X = I, Br, Cl), showing excellent agreement with high field magnetoabsorption and other optical-resolved techniques. The results suggest that the Pollmann-Buttner model offers a robust and novel approach for determining the reduced effective mass in metal tri-halide perovskites and other polar materials exhibiting free exciton bands.},
keywords = {},
pubstate = {published},
tppubtype = {misc}
}
Accurate determination of the exciton binding energy and reduced effective mass in halide perovskites is of utmost importance for the selective design of optoelectronic devices. Although these properties are currently determined by several spectroscopic techniques, complementary theoretical models are often required to bridge macroscopic and microscopic properties. Here, we present a novel method to determine these quantities while fully accounting for polarization effects due to carrier interactions with longitudinal optical phonons. Our approach estimates the exciton-polaron binding energy from optical absorption measurements using a recently developed Elliott based Band Fluctuations model. The reduced effective mass is obtained via the Pollmann-Buttner exciton-polaron model, which is based on the Frohlich polaron framework, where the strength of the electron-phonon interaction arises from changes in the dielectric properties. The procedure is applied to the family of perovskites ABX3 (A = MA, FA, Cs; B = Pb; X = I, Br, Cl), showing excellent agreement with high field magnetoabsorption and other optical-resolved techniques. The results suggest that the Pollmann-Buttner model offers a robust and novel approach for determining the reduced effective mass in metal tri-halide perovskites and other polar materials exhibiting free exciton bands.
Marinho, Enesio; Dias, Alexandre C.; Gomes, Lidia C.; Seridonio, Antonio C. F.; Meira, Gabriel M. C.; Souza, Mariano; Soares, Samuel M.; Squillante, Lucas; Venezuela, Pedro; Rocha, Alexandre R.; Villegas, Cesar E. P.
Optoelectronic properties of boron monochalcogenide monolayers: Quasiparticle and excitonic effects from first principles Journal Article
Em: Phys. Rev. B, vol. 111, não 23, 2025, ISSN: 2469-9969.
@article{Marinho2025,
title = {Optoelectronic properties of boron monochalcogenide monolayers: Quasiparticle and excitonic effects from first principles},
author = {Enesio Marinho and Alexandre C. Dias and Lidia C. Gomes and Antonio C. F. Seridonio and Gabriel M. C. Meira and Mariano Souza and Samuel M. Soares and Lucas Squillante and Pedro Venezuela and Alexandre R. Rocha and Cesar E. P. Villegas},
doi = {10.1103/v37y-njhk},
issn = {2469-9969},
year = {2025},
date = {2025-06-23},
journal = {Phys. Rev. B},
volume = {111},
number = {23},
publisher = {American Physical Society (APS)},
abstract = {We investigate the linear optical response and excitonic landscape in boron monochalcogenide (B𝑋, 𝑋 = S, Se, Te) single layers using ab initio many-body perturbation theory. These 2D monochalcogenides are wide band gap semiconductors, with the valence band exhibiting a quasiflat caldera-shaped dispersion in BS and BSe sheets, associated with strong van Hove singularities at the Fermi level in the density of states, an electronic feature that plays a crucial role in the emergence of strong excitonic effects. By solving the Bethe-Salpeter equation on top of 𝐺0𝑊0 quasiparticle energies, our results reveal that bound excitons arise from direct optical transitions between the highest occupied band and the lowest unoccupied band along the Γ−𝑀 and Γ−𝐾 paths. Additionally, in BS and BSe monolayers, we identify excitons that are bright for in-plane polarized incident light while becoming dark for out-of-plane polarization, and other excitons with the opposite behavior. The optical selection rules are described using group-theory analysis of wave-function symmetries, determining whether optical transitions are dipole allowed or forbidden. Furthermore, exciton radiative lifetimes are estimated to range from 0.2 ns to 1.6 ns at room temperature, while exciton binding energies are significantly high, ranging from 0.6 eV to 1.2 eV for both indirect ground-state excitons and zero-momentum direct excitons. Finally, the strong electron-hole interactions in these materials lead to the formation of tightly bound excitons with a small radius, paving the way for excitonic Bose-Einstein condensation in B𝑋 monolayers. Our study sheds light on the complex excitonic features of single-layer B𝑋, emphasizing its potential for cutting-edge applications in exciton-driven optoelectronics and quantum technologies.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We investigate the linear optical response and excitonic landscape in boron monochalcogenide (B𝑋, 𝑋 = S, Se, Te) single layers using ab initio many-body perturbation theory. These 2D monochalcogenides are wide band gap semiconductors, with the valence band exhibiting a quasiflat caldera-shaped dispersion in BS and BSe sheets, associated with strong van Hove singularities at the Fermi level in the density of states, an electronic feature that plays a crucial role in the emergence of strong excitonic effects. By solving the Bethe-Salpeter equation on top of 𝐺0𝑊0 quasiparticle energies, our results reveal that bound excitons arise from direct optical transitions between the highest occupied band and the lowest unoccupied band along the Γ−𝑀 and Γ−𝐾 paths. Additionally, in BS and BSe monolayers, we identify excitons that are bright for in-plane polarized incident light while becoming dark for out-of-plane polarization, and other excitons with the opposite behavior. The optical selection rules are described using group-theory analysis of wave-function symmetries, determining whether optical transitions are dipole allowed or forbidden. Furthermore, exciton radiative lifetimes are estimated to range from 0.2 ns to 1.6 ns at room temperature, while exciton binding energies are significantly high, ranging from 0.6 eV to 1.2 eV for both indirect ground-state excitons and zero-momentum direct excitons. Finally, the strong electron-hole interactions in these materials lead to the formation of tightly bound excitons with a small radius, paving the way for excitonic Bose-Einstein condensation in B𝑋 monolayers. Our study sheds light on the complex excitonic features of single-layer B𝑋, emphasizing its potential for cutting-edge applications in exciton-driven optoelectronics and quantum technologies.
Villegas, Cesar E. P.; Jr, Enesio Marinho; Dias, A. C.; Venezuela, Pedro; Rocha, Alexandre Reily
Optical properties of TiS3 as a novel thin film for single-junction and tandem solar cells Working paper
2025.
@workingpaper{villegas2025opticalpropertiestis3novel,
title = {Optical properties of TiS3 as a novel thin film for single-junction and tandem solar cells},
author = {Cesar E. P. Villegas and Enesio Marinho Jr and A. C. Dias and Pedro Venezuela and Alexandre Reily Rocha},
url = {https://arxiv.org/abs/2504.06368},
year = {2025},
date = {2025-04-08},
urldate = {2025-01-01},
abstract = {Sub-micrometer thin films are promising platforms for emerging flexible photovoltaic devices. Although the current market already produces efficient solar cells, the average wafer thickness of these devices remains far from the sub-micrometer scale, making them susceptible to cracking under bending stress and thus precluding their use in flexible device applications. Due to its earth abundance, non-toxicity, and low elastic modulus, titanium trisulfide (TiS3) has emerged as a promising alternative for flexible device applications. Here, using excited-state density functional calculations combined with the transfer matrix approach, we perform an optical analysis and assess the efficiency of a prototype photovoltaic device based on sub-micrometer TiS3 thin films. Using optical constants obtained from our first-principles calculations, we evaluate the photovoltaic response of a single-junction device in the radiative limit, finding that a 140-nm-thick active layer achieves a maximum power conversion efficiency of approximately 22%. Additionally, we investigate tandem solar cells that incorporate TiS3 into perovskite thin films, and find that the lower and upper power conversion efficiencies range from approximately 18% to 33%. Overall, our results suggest great potential for using TiS3 thin films as an active layer in the design of highly efficient flexible solar cells.},
keywords = {},
pubstate = {published},
tppubtype = {workingpaper}
}
Sub-micrometer thin films are promising platforms for emerging flexible photovoltaic devices. Although the current market already produces efficient solar cells, the average wafer thickness of these devices remains far from the sub-micrometer scale, making them susceptible to cracking under bending stress and thus precluding their use in flexible device applications. Due to its earth abundance, non-toxicity, and low elastic modulus, titanium trisulfide (TiS3) has emerged as a promising alternative for flexible device applications. Here, using excited-state density functional calculations combined with the transfer matrix approach, we perform an optical analysis and assess the efficiency of a prototype photovoltaic device based on sub-micrometer TiS3 thin films. Using optical constants obtained from our first-principles calculations, we evaluate the photovoltaic response of a single-junction device in the radiative limit, finding that a 140-nm-thick active layer achieves a maximum power conversion efficiency of approximately 22%. Additionally, we investigate tandem solar cells that incorporate TiS3 into perovskite thin films, and find that the lower and upper power conversion efficiencies range from approximately 18% to 33%. Overall, our results suggest great potential for using TiS3 thin films as an active layer in the design of highly efficient flexible solar cells.
Pedrosa, Renan Narciso; Villegas, Cesar E. P.; Rocha, Alexandre Reily; Amorim, Rodrigo G.; Scopel, Wanderlã L.
Interlayer Excitons and Radiative Lifetimes in MoSe2/SeWS Bilayers: Implications for Light-Emitting Diodes Journal Article
Em: ACS Appl. Nano Mater., vol. 8, não 10, pp. 5051–5058, 2025, ISSN: 2574-0970.
@article{NarcisoPedrosa2025,
title = {Interlayer Excitons and Radiative Lifetimes in MoSe2/SeWS Bilayers: Implications for Light-Emitting Diodes},
author = {Renan Narciso Pedrosa and Cesar E. P. Villegas and Alexandre Reily Rocha and Rodrigo G. Amorim and Wanderlã L. Scopel},
url = {https://pubs.acs.org/doi/full/10.1021/acsanm.4c06994},
doi = {10.1021/acsanm.4c06994},
issn = {2574-0970},
year = {2025},
date = {2025-03-14},
urldate = {2025-03-14},
journal = {ACS Appl. Nano Mater.},
volume = {8},
number = {10},
pages = {5051–5058},
publisher = {American Chemical Society (ACS)},
abstract = {Interlayer excitons, formed by electrical charge transfer between layers of 2D van der Waals heterostructures, are of the utmost importance for light-detection and light-harvesting applications. In particular, Janus-based heterostructures are promising platforms to observe robust interlayer exciton dynamics due to their intrinsic electric field. Here, we carry out ground- and excited-state first-principles calculations, based on the G0W0 approach and the solution of the Bethe–Salpeter equation, to investigate the energetic, electronic, and excitonic properties of MoSe2/WSSe van der Waals heterobilayers. Our results show that the heterojunction presents features of type-II band alignment and tightly bound, long-lived interlayer excitons. Indeed, the lowest dipole-allowed excitonic state possesses an interlayer character and a slight deviation of 12% in its binding energy compared to the lowest-energy intralayer exciton. Furthermore, the interlayer excitons have transition rates ∼55 times smaller than the intralayer ones, which translates into a longer radiative lifetime of dozens of nanoseconds at room temperature. This is up to 2 orders of magnitude greater than that of the lowest-energy intralayer exciton. The findings emphasize the critical role of Janus-based heterojunctions in influencing interlayer exciton radiative lifetimes, indicating that the system possesses considerable potential for application in optoelectronic devices such as a light-emitting diode (LED) or photodetector.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Interlayer excitons, formed by electrical charge transfer between layers of 2D van der Waals heterostructures, are of the utmost importance for light-detection and light-harvesting applications. In particular, Janus-based heterostructures are promising platforms to observe robust interlayer exciton dynamics due to their intrinsic electric field. Here, we carry out ground- and excited-state first-principles calculations, based on the G0W0 approach and the solution of the Bethe–Salpeter equation, to investigate the energetic, electronic, and excitonic properties of MoSe2/WSSe van der Waals heterobilayers. Our results show that the heterojunction presents features of type-II band alignment and tightly bound, long-lived interlayer excitons. Indeed, the lowest dipole-allowed excitonic state possesses an interlayer character and a slight deviation of 12% in its binding energy compared to the lowest-energy intralayer exciton. Furthermore, the interlayer excitons have transition rates ∼55 times smaller than the intralayer ones, which translates into a longer radiative lifetime of dozens of nanoseconds at room temperature. This is up to 2 orders of magnitude greater than that of the lowest-energy intralayer exciton. The findings emphasize the critical role of Janus-based heterojunctions in influencing interlayer exciton radiative lifetimes, indicating that the system possesses considerable potential for application in optoelectronic devices such as a light-emitting diode (LED) or photodetector.
2024
Lyu, Peifen; Matusalem, Filipe; Deniz, Ece; Rocha, Alexandre Reily; Leite, Marina S.
In Situ Solid-State Dewetting of Ag–Au–Pd Alloy: From Macro- to Nanoscale Journal Article
Em: ACS Appl. Mater. Interfaces, vol. 16, não 45, pp. 62860–62870, 2024, ISSN: 1944-8252.
@article{Lyu2024,
title = {In Situ Solid-State Dewetting of Ag–Au–Pd Alloy: From Macro- to Nanoscale},
author = {Peifen Lyu and Filipe Matusalem and Ece Deniz and Alexandre Reily Rocha and Marina S. Leite},
doi = {10.1021/acsami.4c11397},
issn = {1944-8252},
year = {2024},
date = {2024-11-13},
urldate = {2024-11-13},
journal = {ACS Appl. Mater. Interfaces},
volume = {16},
number = {45},
pages = {62860–62870},
publisher = {American Chemical Society (ACS)},
abstract = {etal alloy nanostructures represent a promising platform for next-generation nanophotonic devices, surpassing the limitations of pure metals by offering additional “buttons” for tailoring their optical properties by compositional variations. While alloyed nanoparticles hold great potential, their scalability and underexplored optical behavior still limit their application. Here, we establish a systematic approach to quantifying the unique optical behavior of the AgAuPd ternary system while providing a direct comparison with its pure constituent metals. Computationally, we analyze their electronic structure and uncover the transition of Pd d states to Pd/Ag hybridized s states in the bulk form, explaining the similar optical properties observed between Pd and AgAuPd. Experimentally, we fabricate pure metal and fully alloyed nanoparticles through solid-state dewetting, a scalable method. During the process, we trace the optical transition in the systems from the initial thin film stage to the final nanoparticle stage with in situ ellipsometry. We reveal the interplay between optical properties influenced by chemical interdiffusion and localized surface plasmon resonance arising from morphological changes with ex situ surface characterizations. Additionally, we analytically implement a metallic layer derived from the ternary system in a trilayer device, resulting in a single-time and irreversible color filter, to demonstrate an application encompassing a lithography-free and cost-effective route for nanophotonic devices.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
etal alloy nanostructures represent a promising platform for next-generation nanophotonic devices, surpassing the limitations of pure metals by offering additional “buttons” for tailoring their optical properties by compositional variations. While alloyed nanoparticles hold great potential, their scalability and underexplored optical behavior still limit their application. Here, we establish a systematic approach to quantifying the unique optical behavior of the AgAuPd ternary system while providing a direct comparison with its pure constituent metals. Computationally, we analyze their electronic structure and uncover the transition of Pd d states to Pd/Ag hybridized s states in the bulk form, explaining the similar optical properties observed between Pd and AgAuPd. Experimentally, we fabricate pure metal and fully alloyed nanoparticles through solid-state dewetting, a scalable method. During the process, we trace the optical transition in the systems from the initial thin film stage to the final nanoparticle stage with in situ ellipsometry. We reveal the interplay between optical properties influenced by chemical interdiffusion and localized surface plasmon resonance arising from morphological changes with ex situ surface characterizations. Additionally, we analytically implement a metallic layer derived from the ternary system in a trilayer device, resulting in a single-time and irreversible color filter, to demonstrate an application encompassing a lithography-free and cost-effective route for nanophotonic devices.
Arvelos, Graciele M.; Fernández-Serra, Marivi; Rocha, Alexandre Reily; Pedroza, Luana S.
Probing Water-Electrified Electrode interfaces: Insights from Au and Pd Working paper
2024.
@workingpaper{arvelos2024probingwaterelectrifiedelectrodeinterfaces,
title = {Probing Water-Electrified Electrode interfaces: Insights from Au and Pd},
author = {Graciele M. Arvelos and Marivi Fernández-Serra and Alexandre Reily Rocha and Luana S. Pedroza},
url = {https://arxiv.org/abs/2410.24150},
year = {2024},
date = {2024-10-31},
urldate = {2024-01-01},
abstract = {The water/electrode interface under an applied bias potential is a challenging out-of-equilibrium phenomenon, which is difficult to accurately model at the atomic scale. In this study, we employ a combined approach of Density Functional Theory (DFT) and non-equilibrium Green's function (NEGF) methods to analyze the influence of an external bias on the properties of water adsorbed on Au(111) and Pd(111) metallic electrodes. Our results demonstrate that while both Au and Pd-electrodes induce qualitatively similar structural responses in adsorbed water molecules, the quantitative differences are substantial, driven by the distinct nature of water-metal bonding. Our findings underscore the necessity of quantum-mechanical modeling for accurately describing electrochemical interfaces.},
keywords = {},
pubstate = {published},
tppubtype = {workingpaper}
}
The water/electrode interface under an applied bias potential is a challenging out-of-equilibrium phenomenon, which is difficult to accurately model at the atomic scale. In this study, we employ a combined approach of Density Functional Theory (DFT) and non-equilibrium Green's function (NEGF) methods to analyze the influence of an external bias on the properties of water adsorbed on Au(111) and Pd(111) metallic electrodes. Our results demonstrate that while both Au and Pd-electrodes induce qualitatively similar structural responses in adsorbed water molecules, the quantitative differences are substantial, driven by the distinct nature of water-metal bonding. Our findings underscore the necessity of quantum-mechanical modeling for accurately describing electrochemical interfaces.
Marques, Mateus; Melo, Bruno M. Souza; Rocha, Alexandre Reily; Lewenkopf, Caio; Silva, Luis G. G. V. Dias
Suppression of the Mott insulating phase in the particle-hole asymmetric Hubbard model Miscellaneous
2024.
@misc{marques2024suppressionmottinsulatingphase,
title = {Suppression of the Mott insulating phase in the particle-hole asymmetric Hubbard model},
author = {Mateus Marques and Bruno M. Souza Melo and Alexandre Reily Rocha and Caio Lewenkopf and Luis G. G. V. Dias Silva},
url = {https://arxiv.org/abs/2409.06674},
year = {2024},
date = {2024-09-10},
urldate = {2024-01-01},
abstract = {We explore the phase diagram of the Mott metal-insulator transition (MIT), focusing on the effects of particle-hole asymmetry (PHA) in the single-band Hubbard model. Our dynamical mean-field theory (DMFT) study reveals that the introduction of PHA in the model significantly influences the critical temperature (Tc) and interaction strength (Uc), as well as the size of the co-existence region of metallic and insulating phases at low temperatures. Specifically, as the system is moved away from particle-hole symmetry, Tc decreases and Uc increases, indicating a suppression of the insulating phase and the strengthening of the metallic behavior. Additionally, the first-order transition line between metallic and insulating phases is better defined in the model with PHA, leading to a reduced co-existence region at T<Tc. Moreover, we propose that the MIT can be characterized by the charge density, which serves as a viable alternative to zero-frequency spectral density typically used in DMFT calculations. Our findings provide new insights into the role of particle-hole asymmetry in the qualitative and quantitative characterization of the MIT even in a very simple system.},
keywords = {},
pubstate = {published},
tppubtype = {misc}
}
We explore the phase diagram of the Mott metal-insulator transition (MIT), focusing on the effects of particle-hole asymmetry (PHA) in the single-band Hubbard model. Our dynamical mean-field theory (DMFT) study reveals that the introduction of PHA in the model significantly influences the critical temperature (Tc) and interaction strength (Uc), as well as the size of the co-existence region of metallic and insulating phases at low temperatures. Specifically, as the system is moved away from particle-hole symmetry, Tc decreases and Uc increases, indicating a suppression of the insulating phase and the strengthening of the metallic behavior. Additionally, the first-order transition line between metallic and insulating phases is better defined in the model with PHA, leading to a reduced co-existence region at T<Tc. Moreover, we propose that the MIT can be characterized by the charge density, which serves as a viable alternative to zero-frequency spectral density typically used in DMFT calculations. Our findings provide new insights into the role of particle-hole asymmetry in the qualitative and quantitative characterization of the MIT even in a very simple system.
Duarte, F R; Matusalem, F; Grasseschi, D; Rocha, Alexandre Reily; Seixas, Leandro; Matos, Christiano J S; Mukim, S; Ferreira, M S
Decoding disorder signatures of AuCl3 and vacancies in MoS2 films: from synthetic to experimental inversion Journal Article
Em: J. Phys.: Condens. Matter, vol. 36, não 49, 2024, ISSN: 1361-648X.
@article{Duarte2024,
title = {Decoding disorder signatures of AuCl3 and vacancies in MoS2 films: from synthetic to experimental inversion},
author = {F R Duarte and F Matusalem and D Grasseschi and Alexandre Reily Rocha and Leandro Seixas and Christiano J S Matos and S Mukim and M S Ferreira},
url = {https://iopscience.iop.org/article/10.1088/1361-648X/ad7568},
doi = {10.1088/1361-648x/ad7568},
issn = {1361-648X},
year = {2024},
date = {2024-09-01},
urldate = {2024-12-11},
journal = {J. Phys.: Condens. Matter},
volume = {36},
number = {49},
publisher = {IOP Publishing},
abstract = {This study investigates the scope of application of a recently designed inversion methodology that is capable of obtaining structural information about disordered systems through the analysis of their conductivity response signals. Here we demonstrate that inversion tools of this type are capable of sensing the presence of disorderly distributed defects and impurities even in the case where the scattering properties of the device are only weakly affected. This is done by inverting the DC conductivity response of monolayered MoS2 films containing a minute amount of AuCl3 coordinated complexes. Remarkably, we have successfully extracted detailed information about the concentration of AuCl3 by decoding its signatures on the transport features of simulated devices. In addition to the case of theoretically generated Hamiltonians, we have also carried out a full inversion procedure from experimentally measured signals of similar structures. Based on experimental input signals of MoS2 with naturally occurring vacancies, we were able to quantify the vacancy concentration contained in the samples, which indicates that the inversion methodology has experimental applicability as long as the input signal is able to resolve the characteristic contributions of the type of disorder in question. Being able to handle more complex, realistic scenarios unlocks the method's applicability for designing and engineering even more elaborate materials.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
This study investigates the scope of application of a recently designed inversion methodology that is capable of obtaining structural information about disordered systems through the analysis of their conductivity response signals. Here we demonstrate that inversion tools of this type are capable of sensing the presence of disorderly distributed defects and impurities even in the case where the scattering properties of the device are only weakly affected. This is done by inverting the DC conductivity response of monolayered MoS2 films containing a minute amount of AuCl3 coordinated complexes. Remarkably, we have successfully extracted detailed information about the concentration of AuCl3 by decoding its signatures on the transport features of simulated devices. In addition to the case of theoretically generated Hamiltonians, we have also carried out a full inversion procedure from experimentally measured signals of similar structures. Based on experimental input signals of MoS2 with naturally occurring vacancies, we were able to quantify the vacancy concentration contained in the samples, which indicates that the inversion methodology has experimental applicability as long as the input signal is able to resolve the characteristic contributions of the type of disorder in question. Being able to handle more complex, realistic scenarios unlocks the method's applicability for designing and engineering even more elaborate materials.
Marinho, Enesio; Villegas, Cesar E. P.; Venezuela, Pedro; Rocha, Alexandre Reily
Many-Body Effects on Electronic Properties and Optical Response of Single-Layer Penta-NiN2 for Infrared Optoelectronics Journal Article
Em: ACS Appl. Nano Mater., 2024, ISSN: 2574-0970.
@article{Marinho2024,
title = {Many-Body Effects on Electronic Properties and Optical Response of Single-Layer Penta-NiN2 for Infrared Optoelectronics},
author = {Enesio Marinho and Cesar E. P. Villegas and Pedro Venezuela and Alexandre Reily Rocha},
url = {https://pubs.acs.org/doi/full/10.1021/acsanm.4c03019},
doi = {10.1021/acsanm.4c03019},
issn = {2574-0970},
year = {2024},
date = {2024-08-15},
urldate = {2024-08-15},
journal = {ACS Appl. Nano Mater.},
publisher = {American Chemical Society (ACS)},
abstract = {We present a comprehensive first-principles study on the optoelectronic properties of the single-layer nickel diazenide (penta-NiN2), a pentagon-based 2D semiconductor with ideal Cairo tessellation, whose bulk counterpart has been recently synthesized. To address its quasiparticle band structure and excitonic effects on its optical absorption spectrum, we carry out ab initio calculations based on many-body perturbation theory within the GW-Bethe–Salpeter equation (BSE) framework. Our results reveal a quasiparticle band gap of 1.05 eV by employing the eigenvalue self-consistent GW approach, corroborating its potential in optoelectronics. The band gap exhibits an anomalous negative dependence on temperature, verified through the band gap pressure coefficient. Acoustic phonon-limited scattering analyses indicate an ultrahigh hole mobility of ∼87 × 104 cm2 V–1 s–1 along the [010] direction. The most prominent absorption peak of monolayer penta-NiN2 is associated with resonant excitons, corresponding to transitions from the valence band maximum to conduction band minimum + 2, which is explained by analyzing the state symmetry of the band edges. Hence, this pentagonal 2D semiconductor exhibits compelling and promising properties deserving deeper exploration in infrared optoelectronics and high-speed devices.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We present a comprehensive first-principles study on the optoelectronic properties of the single-layer nickel diazenide (penta-NiN2), a pentagon-based 2D semiconductor with ideal Cairo tessellation, whose bulk counterpart has been recently synthesized. To address its quasiparticle band structure and excitonic effects on its optical absorption spectrum, we carry out ab initio calculations based on many-body perturbation theory within the GW-Bethe–Salpeter equation (BSE) framework. Our results reveal a quasiparticle band gap of 1.05 eV by employing the eigenvalue self-consistent GW approach, corroborating its potential in optoelectronics. The band gap exhibits an anomalous negative dependence on temperature, verified through the band gap pressure coefficient. Acoustic phonon-limited scattering analyses indicate an ultrahigh hole mobility of ∼87 × 104 cm2 V–1 s–1 along the [010] direction. The most prominent absorption peak of monolayer penta-NiN2 is associated with resonant excitons, corresponding to transitions from the valence band maximum to conduction band minimum + 2, which is explained by analyzing the state symmetry of the band edges. Hence, this pentagonal 2D semiconductor exhibits compelling and promising properties deserving deeper exploration in infrared optoelectronics and high-speed devices.
Santos, Washington F.; Amorim, Felippe; Rocha, Alexandre Reily
Simulating graphene-based single-electron transistor: incoherent current effects due to the presence of electron-electron interaction Journal Article
Em: 2024.
@article{santos2024simulating,
title = {Simulating graphene-based single-electron transistor: incoherent current effects due to the presence of electron-electron interaction},
author = {Washington F. Santos and Felippe Amorim and Alexandre Reily Rocha},
url = {https://arxiv.org/abs/2405.14003v1},
doi = {https://doi.org/10.48550/arXiv.2405.14003},
year = {2024},
date = {2024-05-22},
urldate = {2024-01-01},
abstract = {Carbon-based nanostructures have unparalleled electronic properties. At the same time, using an allotrope of carbon as the contacts can yield better device control and reproducibility. In this work, we simulate a single-electron transistor composed of a segment of a graphene nanoribbon coupled to carbon nanotubes electrodes. Using the non-equilibrium Green's function formalism we atomistically describe the electronic transport properties of the system including electron-electron interactions. Using this methodology we are able to recover experimentally observed phenomena, such as the Coulomb blockade, as well as the corresponding Coulomb diamonds. Furthermore, we are able to separate the different contributions to transport and show that incoherent effects due to the interaction play a crucial role in the transport properties depending on the region of the stability diagram being considered.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Carbon-based nanostructures have unparalleled electronic properties. At the same time, using an allotrope of carbon as the contacts can yield better device control and reproducibility. In this work, we simulate a single-electron transistor composed of a segment of a graphene nanoribbon coupled to carbon nanotubes electrodes. Using the non-equilibrium Green's function formalism we atomistically describe the electronic transport properties of the system including electron-electron interactions. Using this methodology we are able to recover experimentally observed phenomena, such as the Coulomb blockade, as well as the corresponding Coulomb diamonds. Furthermore, we are able to separate the different contributions to transport and show that incoherent effects due to the interaction play a crucial role in the transport properties depending on the region of the stability diagram being considered.
Villegas, Cesar EP; Vasquez-Marcani, Aider; Rocha, Alexandre Reily
Static dielectric response and screening in solid state physics: Why dimensionality matters in dielectrics Journal Article
Em: American Journal of Physics, vol. 92, não 5, pp. 360–366, 2024.
@article{villegas2024static,
title = {Static dielectric response and screening in solid state physics: Why dimensionality matters in dielectrics},
author = {Cesar EP Villegas and Aider Vasquez-Marcani and Alexandre Reily Rocha},
url = {https://pubs.aip.org/aapt/ajp/article-abstract/92/5/360/3283200/Static-dielectric-response-and-screening-in-solid?redirectedFrom=fulltext},
doi = {https://doi.org/10.1119/5.0122288},
year = {2024},
date = {2024-05-01},
urldate = {2024-01-01},
journal = {American Journal of Physics},
volume = {92},
number = {5},
pages = {360–366},
publisher = {AIP Publishing},
abstract = {Textbooks often present the phenomenon of screening within the Thomas–Fermi model for three-dimensional free electron gases, but obtaining the dielectric response function and screening potential for dielectric systems of reduced dimensionality is also of pedagogical interest. In this work, we introduce a simple approach to investigate static screening in dielectric systems in the presence of an impurity charge for different dimensionalities. This approach is applicable to semiconductors and insulators alike. We demonstrate that, in 3D systems, the macroscopic dielectric function in reciprocal space is a constant, while in 2D and 1D systems, it strongly depends on the momentum transferred to the electrons in the dielectric. Through the proposed dielectric screening model, one can also determine binding energies in a hydrogenic model that can be used to describe excitations in real semiconductor systems.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Textbooks often present the phenomenon of screening within the Thomas–Fermi model for three-dimensional free electron gases, but obtaining the dielectric response function and screening potential for dielectric systems of reduced dimensionality is also of pedagogical interest. In this work, we introduce a simple approach to investigate static screening in dielectric systems in the presence of an impurity charge for different dimensionalities. This approach is applicable to semiconductors and insulators alike. We demonstrate that, in 3D systems, the macroscopic dielectric function in reciprocal space is a constant, while in 2D and 1D systems, it strongly depends on the momentum transferred to the electrons in the dielectric. Through the proposed dielectric screening model, one can also determine binding energies in a hydrogenic model that can be used to describe excitations in real semiconductor systems.
Villegas, Cesar E. P.; Marinho, Enesio; Venezuela, Pedro; Rocha, Alexandre Reily
Optical spectra and exciton radiative lifetimes in bulk transition metal dichalcogenides Journal Article
Em: Phys. Chem. Chem. Phys., pp. -, 2024.
@article{D3CP05949A,
title = {Optical spectra and exciton radiative lifetimes in bulk transition metal dichalcogenides},
author = {Cesar E. P. Villegas and Enesio Marinho and Pedro Venezuela and Alexandre Reily Rocha},
url = {http://dx.doi.org/10.1039/D3CP05949A},
doi = {10.1039/D3CP05949A},
year = {2024},
date = {2024-04-16},
urldate = {2024-01-01},
journal = {Phys. Chem. Chem. Phys.},
pages = {-},
publisher = {The Royal Society of Chemistry},
abstract = {The optical response of layered transition metal dichalcogenides (TMDCs) exhibits remarkable excitonic properties which are important from both fundamental and device application viewpoints. One of these phenomena is the observation of intralayer/interlayer excitons. While much effort has been done to characterize excitons in monolayer TMDCs and their heterostructures, a quite limited number of works have addressed the exciton spectra of their bulk counterparts. In this work, we employ ab initio many-body perturbation calculations to investigate the exciton dynamics and spectra of bulk 2H-MX2 (M = Mo, W, and X = S, Se). For molybdenum-based systems, we find the presence of interlayer excitons at energies higher than the first bright exciton (XA), with non-negligible strength intensity. Our results also show that interlayer excitons in tungsten-based systems are almost degenerate in energy with XA and possess very small oscillator strengths when compared with molybdenum-based systems. At room temperature, and considering the thermal exciton fine-structure population for the XA-exciton, we estimate effective radiative lifetimes in the range of ∼4–14 ns. For higher energy excitons we predict longer effective lifetimes of tens of nanoseconds.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The optical response of layered transition metal dichalcogenides (TMDCs) exhibits remarkable excitonic properties which are important from both fundamental and device application viewpoints. One of these phenomena is the observation of intralayer/interlayer excitons. While much effort has been done to characterize excitons in monolayer TMDCs and their heterostructures, a quite limited number of works have addressed the exciton spectra of their bulk counterparts. In this work, we employ ab initio many-body perturbation calculations to investigate the exciton dynamics and spectra of bulk 2H-MX2 (M = Mo, W, and X = S, Se). For molybdenum-based systems, we find the presence of interlayer excitons at energies higher than the first bright exciton (XA), with non-negligible strength intensity. Our results also show that interlayer excitons in tungsten-based systems are almost degenerate in energy with XA and possess very small oscillator strengths when compared with molybdenum-based systems. At room temperature, and considering the thermal exciton fine-structure population for the XA-exciton, we estimate effective radiative lifetimes in the range of ∼4–14 ns. For higher energy excitons we predict longer effective lifetimes of tens of nanoseconds.
Pedrosa, Renan Narciso; Villegas, Cesar EP; Rocha, Alexandre Reily; Amorim, Rodrigo G.; Scopel, Wanderlã L.
Optical properties enhancement via WSSe/silicene solar cell junctions Journal Article
Em: Energy Advances, vol. 3, não 4, pp. 821–828, 2024.
@article{pedrosa2024optical,
title = {Optical properties enhancement via WSSe/silicene solar cell junctions},
author = {Renan Narciso Pedrosa and Cesar EP Villegas and Alexandre Reily Rocha and Rodrigo G. Amorim and Wanderlã L. Scopel},
url = {https://pubs.rsc.org/en/content/articlehtml/2024/ya/d3ya00529a},
doi = {10.1039/D3YA00529A},
year = {2024},
date = {2024-03-04},
urldate = {2024-03-04},
journal = {Energy Advances},
volume = {3},
number = {4},
pages = {821–828},
publisher = {Royal Society of Chemistry},
abstract = {2D Janus monolayers exhibit nanoscale asymmetric surface organization along the out-of-plane direction and have recently emerged as a class of 2D materials. In this work, we investigate the energetic, electronic, and optical properties of the vertical van der Waals stack between WSSe and silicene monolayers based on first-principles calculations. The Janus/silicene interface formation is driven by an exothermic process, and charge transfer from the silicene to the Janus monolayer is observed. The intrinsic properties of silicene and Janus are preserved despite the stacking of the parts. The Bethe–Salpeter equation (BSE) was used to understand the contact influence on the optical absorption spectrum of the vertical interface. Our findings reveal that the power conversion energy (PCE) of the heterostructure is boosted 2.42 times higher than that of the Janus monolayer. Thus, due to its PCE and transparent electrical contact, the heterojunction is a promising candidate for use as a photovoltaic device compared to its counterparts.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
2D Janus monolayers exhibit nanoscale asymmetric surface organization along the out-of-plane direction and have recently emerged as a class of 2D materials. In this work, we investigate the energetic, electronic, and optical properties of the vertical van der Waals stack between WSSe and silicene monolayers based on first-principles calculations. The Janus/silicene interface formation is driven by an exothermic process, and charge transfer from the silicene to the Janus monolayer is observed. The intrinsic properties of silicene and Janus are preserved despite the stacking of the parts. The Bethe–Salpeter equation (BSE) was used to understand the contact influence on the optical absorption spectrum of the vertical interface. Our findings reveal that the power conversion energy (PCE) of the heterostructure is boosted 2.42 times higher than that of the Janus monolayer. Thus, due to its PCE and transparent electrical contact, the heterojunction is a promising candidate for use as a photovoltaic device compared to its counterparts.
Villegas, Cesar E. P.; Rocha, Alexandre Reily
Screened hydrogen model of excitons in semiconducting nanoribbons Working paper
2024.
@workingpaper{villegas2024screened,
title = {Screened hydrogen model of excitons in semiconducting nanoribbons},
author = {Cesar E. P. Villegas and Alexandre Reily Rocha},
url = {https://arxiv.org/abs/2403.15793},
doi = {https://doi.org/10.48550/arXiv.2403.15793},
year = {2024},
date = {2024-01-23},
urldate = {2024-01-01},
abstract = {The optical response of quasi-one-dimensional systems is often dominated by tightly bound excitons, that significantly influence their basic electronic properties. Despite their importance for device performance, accurately predicting their excitonic effects typically requires computationally demanding many-body approaches. Here, we present a simplified model to describe the static macroscopic dielectric function, which depends only on the width of the quasi-one-dimensional system and its polarizability per unit length. We show that at certain interaction distances, the screened Coulomb potential is greater than its bare counterpart, which results from the enhanced repulsive electron-electron interactions. As a test case, we study fourteen different nanoribbons, twelve of them armchair graphene nanoribbons of different families. Initially, we devised a simplified equation to estimate the exciton binding energy and extension that provides results comparable to those from the full Bethe-Salpeter equation, albeit for a specific nanoribbon family. Then, we used our proposed screening potential to solve the 1D Wannier-Mott equation, which turn out to be broad approach, that is able to predict binding energies that match quite well the ones obtained with the Bethe-Salpeter equation, irrespective of the nanoribbon family.},
keywords = {},
pubstate = {published},
tppubtype = {workingpaper}
}
The optical response of quasi-one-dimensional systems is often dominated by tightly bound excitons, that significantly influence their basic electronic properties. Despite their importance for device performance, accurately predicting their excitonic effects typically requires computationally demanding many-body approaches. Here, we present a simplified model to describe the static macroscopic dielectric function, which depends only on the width of the quasi-one-dimensional system and its polarizability per unit length. We show that at certain interaction distances, the screened Coulomb potential is greater than its bare counterpart, which results from the enhanced repulsive electron-electron interactions. As a test case, we study fourteen different nanoribbons, twelve of them armchair graphene nanoribbons of different families. Initially, we devised a simplified equation to estimate the exciton binding energy and extension that provides results comparable to those from the full Bethe-Salpeter equation, albeit for a specific nanoribbon family. Then, we used our proposed screening potential to solve the 1D Wannier-Mott equation, which turn out to be broad approach, that is able to predict binding energies that match quite well the ones obtained with the Bethe-Salpeter equation, irrespective of the nanoribbon family.
2023
au2, Enesio Marinho Jr.; Villegas, Cesar E. P.; Venezuela, Pedro; Rocha, Alexandre Reily
Photovoltaic efficiency of transition metal dichalcogenides thin films by ab initio excited-state methods Working paper
2023.
@workingpaper{marinho2023photovoltaic,
title = {Photovoltaic efficiency of transition metal dichalcogenides thin films by ab initio excited-state methods},
author = {Enesio Marinho Jr. au2 and Cesar E. P. Villegas and Pedro Venezuela and Alexandre Reily Rocha},
url = {https://arxiv.org/abs/2312.10284},
doi = {https://doi.org/10.48550/arXiv.2312.10284},
year = {2023},
date = {2023-12-16},
urldate = {2023-01-01},
abstract = {Transition metal dichalcogenides (TMDCs) have garnered significant interest in optoelectronics, owing to their scalability and thickness-dependent electrical and optical properties. In particular, thin films of TMDCs could be used in photovoltaic devices. In this work, we employ ab initio many-body perturbation theory within G0W0-BSE approach to accurately compute the optoelectronic properties of thin films of 2H-TMDCs composed of Mo, W, S, and Se. Subsequently, we evaluate their photovoltaic performance including exciton recombination effects, and show this is a key ingredient. We obtain efficiencies of up to 29% for a 200-nm thick film of ceWSe2, thus providing an upper limit. We also include other textcolorblackphenomenological recombination mechanisms that could be present in current samples. This slightly reduces efficiencies, indicating that even with current synthesis technologies, there is still potential for further enhancement of TMDCs' performance in photovoltaic applications.},
keywords = {},
pubstate = {published},
tppubtype = {workingpaper}
}
Transition metal dichalcogenides (TMDCs) have garnered significant interest in optoelectronics, owing to their scalability and thickness-dependent electrical and optical properties. In particular, thin films of TMDCs could be used in photovoltaic devices. In this work, we employ ab initio many-body perturbation theory within G0W0-BSE approach to accurately compute the optoelectronic properties of thin films of 2H-TMDCs composed of Mo, W, S, and Se. Subsequently, we evaluate their photovoltaic performance including exciton recombination effects, and show this is a key ingredient. We obtain efficiencies of up to 29% for a 200-nm thick film of ceWSe2, thus providing an upper limit. We also include other textcolorblackphenomenological recombination mechanisms that could be present in current samples. This slightly reduces efficiencies, indicating that even with current synthesis technologies, there is still potential for further enhancement of TMDCs' performance in photovoltaic applications.
Jr., Enesio Marinho; Villegas, Cesar E. P.; Venezuela, Pedro; Rocha, Alexandre Reily
Many-body effects on the quasiparticle band structure and optical response of single-layer penta-NiN$_2$ Working paper
2023.
@workingpaper{marinho2023manybody,
title = {Many-body effects on the quasiparticle band structure and optical response of single-layer penta-NiN$_2$},
author = {Enesio Marinho Jr. and Cesar E. P. Villegas and Pedro Venezuela and Alexandre Reily Rocha},
url = {https://arxiv.org/abs/2312.06394},
doi = {https://doi.org/10.48550/arXiv.2312.06394},
year = {2023},
date = {2023-12-11},
urldate = {2023-12-11},
abstract = {We present a comprehensive first-principles study on the optoelectronic properties of the single-layer nickel diazenide (penta-NiN2), a recently synthesized Cairo pentagonal 2D semiconductor. We carry out ab initio calculations based on the density-functional theory (DFT) and many-body perturbation theory, within the framework of Green's functions, to describe the quasiparticle properties and analyze the excitonic effects on the optical properties of monolayer penta-NiN2. Our results reveal a quasiparticle band gap of approximately 1 eV within the eigenvalue self-consistent GW approach, corroborating the monolayer penta-NiN2's potential in optoelectronics. Remarkably, the acoustic phonon-limited carrier mobility for the monolayer penta-NiN2 exhibits an ultra-high hole mobility of 84×104 cm2/V⋅s. Furthermore, our findings indicate that the material's band gap exhibits an anomalous negative dependence on temperature. Despite being a two-dimensional material, monolayer penta-NiN2 presents resonant excitons in its most prominent absorption peak. Therefore, penta-NiN2 boasts compelling and promising properties that merit exploration in optoelectronics and high-speed devices.},
keywords = {},
pubstate = {published},
tppubtype = {workingpaper}
}
We present a comprehensive first-principles study on the optoelectronic properties of the single-layer nickel diazenide (penta-NiN2), a recently synthesized Cairo pentagonal 2D semiconductor. We carry out ab initio calculations based on the density-functional theory (DFT) and many-body perturbation theory, within the framework of Green's functions, to describe the quasiparticle properties and analyze the excitonic effects on the optical properties of monolayer penta-NiN2. Our results reveal a quasiparticle band gap of approximately 1 eV within the eigenvalue self-consistent GW approach, corroborating the monolayer penta-NiN2's potential in optoelectronics. Remarkably, the acoustic phonon-limited carrier mobility for the monolayer penta-NiN2 exhibits an ultra-high hole mobility of 84×104 cm2/V⋅s. Furthermore, our findings indicate that the material's band gap exhibits an anomalous negative dependence on temperature. Despite being a two-dimensional material, monolayer penta-NiN2 presents resonant excitons in its most prominent absorption peak. Therefore, penta-NiN2 boasts compelling and promising properties that merit exploration in optoelectronics and high-speed devices.
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.
Gomes-Filho, Márcio S.; Torres, Alberto; Rocha, Alexandre Reily; Pedroza, Luana S.
Size and Quality of Quantum Mechanical Data Set for Training Neural Network Force Fields for Liquid Water Journal Article
Em: The Journal of Physical Chemistry B, vol. 127, não 6, pp. 1422-1428, 2023, (PMID: 36730848).
@article{doi:10.1021/acs.jpcb.2c09059,
title = {Size and Quality of Quantum Mechanical Data Set for Training Neural Network Force Fields for Liquid Water},
author = {Márcio S. Gomes-Filho and Alberto Torres and Alexandre Reily Rocha and Luana S. Pedroza},
url = {https://doi.org/10.1021/acs.jpcb.2c09059},
doi = {10.1021/acs.jpcb.2c09059},
year = {2023},
date = {2023-01-01},
journal = {The Journal of Physical Chemistry B},
volume = {127},
number = {6},
pages = {1422-1428},
abstract = {Molecular dynamics simulations have been used in different scientific fields to investigate a broad range of physical systems. However, the accuracy of calculation is based on the model considered to describe the atomic interactions. In particular, ab initio molecular dynamics (AIMD) has the accuracy of density functional theory (DFT) and thus is limited to small systems and a relatively short simulation time. In this scenario, Neural Network Force Fields (NNFFs) have an important role, since they provide a way to circumvent these caveats. In this work, we investigate NNFFs designed at the level of DFT to describe liquid water, focusing on the size and quality of the training data set considered. We show that structural properties are less dependent on the size of the training data set compared to dynamical ones (such as the diffusion coefficient), and a good sampling (selecting data reference for the training process) can lead to a small sample with good precision.},
note = {PMID: 36730848},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Molecular dynamics simulations have been used in different scientific fields to investigate a broad range of physical systems. However, the accuracy of calculation is based on the model considered to describe the atomic interactions. In particular, ab initio molecular dynamics (AIMD) has the accuracy of density functional theory (DFT) and thus is limited to small systems and a relatively short simulation time. In this scenario, Neural Network Force Fields (NNFFs) have an important role, since they provide a way to circumvent these caveats. In this work, we investigate NNFFs designed at the level of DFT to describe liquid water, focusing on the size and quality of the training data set considered. We show that structural properties are less dependent on the size of the training data set compared to dynamical ones (such as the diffusion coefficient), and a good sampling (selecting data reference for the training process) can lead to a small sample with good precision.
Amorim, Felippe P.; Torres, Alberto; Villegas, Cesar E. P.; Rocha, Alexandre Reily
Gate voltage enhances the thermoelectric transport of quantum dots in graphene nanoribbons Journal Article
Em: Computational Materials Science, vol. 227, pp. 112207, 2023, ISSN: 0927-0256.
@article{AMORIM2023112207,
title = {Gate voltage enhances the thermoelectric transport of quantum dots in graphene nanoribbons},
author = {Felippe P. Amorim and Alberto Torres and Cesar E. P. Villegas and Alexandre Reily Rocha},
url = {https://www.sciencedirect.com/science/article/pii/S092702562300201X},
doi = {https://doi.org/10.1016/j.commatsci.2023.112207},
issn = {0927-0256},
year = {2023},
date = {2023-01-01},
urldate = {2023-01-01},
journal = {Computational Materials Science},
volume = {227},
pages = {112207},
abstract = {Chemically derived graphene nanoribbons and quantum dots are unique nanostructures that offer more possibilities than 2D and 3D systems to tune their electronic properties due to the enhanced quantum confinement effects. This feature make them potential candidates for many technological applications, including thermoelectrics. In this work, we combined density functional theory calculations with the non-equilibrium Green’s function formalism to investigate the electronic and thermoelectric properties of recently synthesized quantum dots in graphene nanoribbons under the presence of an applied gate voltage, and for different temperatures. We find that the electronic states at the band edge are highly localized in the inner region of the quantum dot, and can be lifted to higher energies by applying a gate voltage, which subsequently enhances figure of merit. Moreover, at zero gate voltage and room temperature, we estimate the lower bound for ZT to be approximately 0.25. Interestingly, this lower bound can exceed unity by smoothly increasing the gate voltage for values above 6 V. The overall results regarding the enhancement of ZT suggest that quantum dots in graphene nanoribbons would be promising candidates for thermoelectric applications.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Chemically derived graphene nanoribbons and quantum dots are unique nanostructures that offer more possibilities than 2D and 3D systems to tune their electronic properties due to the enhanced quantum confinement effects. This feature make them potential candidates for many technological applications, including thermoelectrics. In this work, we combined density functional theory calculations with the non-equilibrium Green’s function formalism to investigate the electronic and thermoelectric properties of recently synthesized quantum dots in graphene nanoribbons under the presence of an applied gate voltage, and for different temperatures. We find that the electronic states at the band edge are highly localized in the inner region of the quantum dot, and can be lifted to higher energies by applying a gate voltage, which subsequently enhances figure of merit. Moreover, at zero gate voltage and room temperature, we estimate the lower bound for ZT to be approximately 0.25. Interestingly, this lower bound can exceed unity by smoothly increasing the gate voltage for values above 6 V. The overall results regarding the enhancement of ZT suggest that quantum dots in graphene nanoribbons would be promising candidates for thermoelectric applications.
2018
Rocha, C. G.; Rocha, A. R.; Venezuela, P.; Garcia, J. H.; Ferreira, M. S.
Finite-size correction scheme for supercell calculations in Dirac-point two-dimensional materials Journal Article
Em: Sci Rep, vol. 8, não 1, 2018, ISSN: 2045-2322.
@article{Rocha2018,
title = {Finite-size correction scheme for supercell calculations in Dirac-point two-dimensional materials},
author = {C. G. Rocha and A. R. Rocha and P. Venezuela and J. H. Garcia and M. S. Ferreira},
doi = {10.1038/s41598-018-27632-6},
issn = {2045-2322},
year = {2018},
date = {2018-12-01},
journal = {Sci Rep},
volume = {8},
number = {1},
publisher = {Springer Science and Business Media LLC},
abstract = {<jats:title>Abstract</jats:title><jats:p>Modern electronic structure calculations are predominantly implemented within the super cell representation in which unit cells are periodically arranged in space. Even in the case of non-crystalline materials, defect-embedded unit cells are commonly used to describe doped structures. However, this type of computation becomes prohibitively demanding when convergence rates are sufficiently slow and may require calculations with very large unit cells. Here we show that a hitherto unexplored feature displayed by several 2D materials may be used to achieve convergence in formation- and adsorption-energy calculations with relatively small unit-cell sizes. The generality of our method is illustrated with Density Functional Theory calculations for different 2D hosts doped with different impurities, all of which providing accuracy levels that would otherwise require enormously large unit cells. This approach provides an efficient route to calculating the physical properties of 2D systems in general but is particularly suitable for Dirac-point materials doped with impurities that break their sublattice symmetry.</jats:p>},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
<jats:title>Abstract</jats:title><jats:p>Modern electronic structure calculations are predominantly implemented within the super cell representation in which unit cells are periodically arranged in space. Even in the case of non-crystalline materials, defect-embedded unit cells are commonly used to describe doped structures. However, this type of computation becomes prohibitively demanding when convergence rates are sufficiently slow and may require calculations with very large unit cells. Here we show that a hitherto unexplored feature displayed by several 2D materials may be used to achieve convergence in formation- and adsorption-energy calculations with relatively small unit-cell sizes. The generality of our method is illustrated with Density Functional Theory calculations for different 2D hosts doped with different impurities, all of which providing accuracy levels that would otherwise require enormously large unit cells. This approach provides an efficient route to calculating the physical properties of 2D systems in general but is particularly suitable for Dirac-point materials doped with impurities that break their sublattice symmetry.</jats:p>
Orientandos
Pós-Doutorado Júnior 2
Larissa Maria Pereira Inacio
IFT-UNESP
Desenvolvimento de potenciais interatômicos baseados em Machine Learning para modelagem de interações de longo alcance em sistemas aquosos
Renan Narciso Pedrosa
UNESP – IFT
Estudo sistemático de propriedades ópticas e eletrônicas em perovskitas de haletos na presença de defeitos: combinando aprendizado de máquina e a Equação de Bethe-Salpeter