arXiv subjects

Gabriela Herrero-Saboya

Publications and source records attributed to Gabriela Herrero-Saboya.

5 recordsLinked to original sources

arXiv2026

Elastic properties of cubic silicon carbide with Si vacancies

We investigate how silicon vacancies modify the elastic response and mechanical stability of cubic 3C-SiC. Our approach employs path-integral molecular dynamics simulations, including the classical-nuclei limit, based on an efficient tight-binding Hamiltonian, whose accuracy is validated against density-functional-theory calculations. This framework enables a quantitative assessment of nuclear quantum effects arising from zero-point motion. Across a broad range of temperatures and hydrostatic pressures, spanning both tensile and compressive regimes, silicon vacancies are found to substantially renormalize the elastic constants $C_{11}$, $C_{12}$, and $C_{44}$, as well as the bulk modulus, relative to the defect-free crystal. Inclusion of nuclear quantum motion produces an additional softening of these elastic properties, particularly at low temperatures, demonstrating that quantum fluctuations make a measurable contribution to the mechanical response of defective SiC. Vacancies also affect the mechanical stability domain of 3C-SiC, lowering the maximum sustainable tensile pressure by approximately 4 GPa for a defect concentration of 0.016 per lattice site. These results reveal an interplay between point defects and quantum lattice fluctuations in determining the elastic behavior of SiC, providing microscopic insight relevant for both extreme-environment structural applications and defect-based quantum technologies.

cond-mat.mtrl-sci↗

arXiv2025

An accurate alternative to hybrid functionals for germanium: DFT+$α$

The accuracy of bulk property predictions in density functional theory (DFT) calculations depends on the choice of exchange-correlation functional. While the Perdew-Burke-Ernzerhof (PBE) functional systematically overestimates lattice parameters and strongly underestimates electronic band gaps, hybrid functionals such as Heyd-Scuseria-Ernzerhof (HSE) offer better overall agreement across a broad range of materials. Using germanium as a critical test case, we challenge the ability of both functionals to capture semiconductor properties. Although HSE improves PBE's gap error, it fails to reproduce germanium's correct $Γ$-L indirect and $Γ$-$Γ$ band gaps simultaneously. Noting that the PBE underestimated energy separation between the 4p valence-band maximum and 4s conduction-band minimum causes unphysical $sp$ mixing, we propose DFT+$α$, a semi-empirical correction scheme applied selectively to 4s-like orbitals. For germanium, DFT+$α$ restores the proper ordering and orbital character of the band edges and yields accurate lattice constant, bulk modulus, elastic constants and phonon frequencies at a fraction of hybrid-functional computational cost.

cond-mat.mtrl-sci↗

arXiv2025

Pressure-Induced Mechanical Instabilities in Cubic SiC: Structural and Electronic Properties

Silicon carbide is widely used in electronics, ceramics, and renewable energy due to its exceptional hardness and resistance. In this study, we investigate the effects of hydrostatic and uniaxial pressure (both compressive and tensile) on the structural and electronic properties of $3C$-SiC. Our analysis is based on atomistic molecular dynamics (MD) simulations using an efficient tight-binding Hamiltonian, whose accuracy is validated against density functional theory calculations. Moreover, to account for nuclear quantum effects, we employ path-integral MD simulations. Our results show significant changes in the direct electronic gap as a function of temperature and pressure, with a renormalization of about 80 meV due to zero-point motion. Under hydrostatic tensile pressure, the direct band gap $E_Γ$ vanishes at the material's mechanical stability limit (spinodal point, where the bulk modulus $B \to 0$). For uniaxial pressure, we observe instabilities (Young's modulus $Y \to 0$) at approximately 90 GPa for both tension and compression, where $E_Γ \to 0$. Additionally, we analyze the pressure dependence of the internal energy, lattice parameter, and bond length, along with their finite-temperature fluctuations, which exhibit anomalies near the instability points.

cond-mat.mtrl-sci↗

arXiv2024

Nuclear quantum effects in structural and elastic properties of cubic silicon carbide

Silicon carbide, a semiconducting material, has gained importance in the fields of ceramics, electronics, and renewable energy due to its remarkable hardness and resistance. In this study, we delve into the impact of nuclear quantum motion, or vibrational mode quantization, on the structural and elastic properties of 3C-SiC. This aspect, elusive in conventional {\it ab-initio} calculations, is explored through path-integral molecular dynamics (PIMD) simulations using an efficient tight-binding (TB) Hamiltonian. This investigation spans a wide range of temperatures and pressures, including tensile stress, adeptly addressing the quantization and anharmonicity inherent in solid-state vibrational modes. The accuracy of the TB model has been checked by comparison with density-functional-theory calculations at zero temperature. The magnitude of quantum effects is assessed by comparing PIMD outcomes with results obtained from classical molecular dynamics simulations. Our investigation uncovers notable reductions of 5%, 10%, and 4% in the elastic constants $C_{11}$, $C_{12}$, and $C_{44}$, respectively, attributed to atomic zero-point oscillations. Consequently, the bulk modulus and Poisson's ratio of 3C-SiC exhibit reduced values by 7% and 5% at low temperature. The persistence of these quantum effects in the material's structural and elastic attributes beyond room temperature underscores the necessity of incorporating nuclear quantum motion for an accurate description of these fundamental properties of SiC.

cond-mat.mtrl-sci↗

arXiv2023

Cubic silicon carbide under tensile pressure: Spinodal instability

Silicon carbide is a hard, semiconducting material presenting many polytypes, whose behavior under extreme conditions of pressure and temperature has attracted large interest. Here we study the mechanical properties of 3C-SiC over a wide range of pressures (compressive and tensile) by means of molecular dynamics simulations, using an effective tight-binding Hamiltonian to describe the interatomic interactions. The accuracy of this procedure has been checked by comparing results at T = 0 with those derived from ab-initio density-functional-theory calculations. This has allowed us to determine the metastability limits of this material and in particular the spinodal point (where the bulk modulus vanishes) as a function of temperature. At T = 300 K, the spinodal instability appears for a lattice parameter about 20% larger than that corresponding to ambient pressure. At this temperature, we find a spinodal pressure P_s = -43 GPa, which becomes less negative as temperature is raised (P_s = -37.9 GPa at 1500 K). These results pave the way for a deeper understanding of the behavior of crystalline semiconductors in a poorly known region of their phase diagrams.

cond-mat.mtrl-sci↗