arXiv subjects

César Castillo-Quevedo

Publications and source records attributed to César Castillo-Quevedo.

4 recordsLinked to original sources

arXiv2026

Optical spin injection in graphane and fluorographene

We theoretically investigate the optical spin-injection response in different stoichiometric configurations of graphane and fluorographene using density functional theory. Our goal is to determine which configuration yields the strongest degree of spin polarization. The results show that the fluorographene zigzag configuration yields the best degree of spin polarization response (${\cal DSP}^{\mathrm{z}}$), with 98\% spin polarized electrons at the band edge and over a wide range of excitation photon energies. In contrast, other graphane and fluorographene configurations achieve a ${\cal DSP}^{\mathrm{z}}$ of roughly 83--100\%, but only within a limited photon-excitation energy range. In structures with low spin-orbit coupling, the degree of spin polarization is close to 100\% over a wide range of photon energies. For higher spin-orbit coupling, this strong response appears, but only in a narrow photon energy region. Additionally, under the band-resolved decomposition scheme, the contributions of different band-to-band transitions to the ${\cal DSP}^{\mathrm{z}}$ spectrum are identified by summing only the selected valence and conduction bands. Our findings show that almost the entire ${\cal DSP}^{\mathrm{z}}$ spectrum of the fluorographene zigzag configuration comes from transitions that involve only the top valence band, which is a mixture of C--p and F--p states.

cond-mat.mes-hall↗

arXiv2026

Unveiling AlSb as a Promising Zincblende Semiconductor for Visible-Light Shift-Current Generation

We use density functional theory to investigate the shift-current response in zincblende III--V (AlP, AlAs, AlSb, GaP, GaAs, InP, InAs, and InSb) and II--VI (ZnS, ZnSe, ZnTe, CdS, CdSe, and CdTe) semiconductors. Our main goal is to identify which material generates the largest shift-current under illumination and to examine the factors influencing this response. We find that aluminum-containing semiconductors, particularly AlSb, exhibit the highest shift-current responses, while CdSe shows the lowest. We analyze the contributions of specific band-to-band transitions to the shift-current in AlSb by selectively summing valence and conduction bands. Additionally, we calculate delocalization indices to investigate the electron delocalization, which correlates with the shift current. Hydrostatic pressure does not enhance the shift current in these materials. These findings have potential applications in optoelectronics and identify the most promising zincblende semiconductors for efficient shift-current generation under visible-light illumination

cond-mat.mtrl-sci↗

arXiv2024

Structures and infrared spectroscopy of Au$_{10}$ cluster at different temperatures

Understanding the properties of Au$_{10}$ clusters entails identifying the lowest energy structure at cold and warm temperatures. While functional materials operate at finite temperatures, energy computations using density functional theory are typically performed at zero temperature, resulting in unexplored properties. Our study undertook an exploration of the potential and free energy surface of the neutral Au$_{10}$ nanocluster at finite temperatures by employing a genetic algorithm combined with density functional theory and nanothermodynamics. We computed the thermal population and infrared Boltzmann spectrum at a finite temperature, aligning the results with validated experimental data. The Zero-Order Regular Approximation (ZORA) gave consideration to relativistic effects, and dispersion was incorporated using Grimme's dispersion D3BJ with Becke-Johnson damping. Moreover, nanothermodynamics was utilized to account for temperature contributions. The computed thermal population strongly supports the dominance of the 2D elongated hexagon configuration within a temperature range of 50 to 800 K. Importantly, at a temperature of 100 K, the calculated IR Boltzmann spectrum aligns with the experimental IR spectrum. Lastly, the chemical bonding analysis on the lowest energy structure indicates a closed-shell Au-Au interaction with a weak or partially covalent character.

cond-mat.mtrl-sci↗

arXiv2022

Structures and stability of the Cu$_{38}$ cluster at finite temperature

The UV-visible and IR properties of the Cu$_{38}$ nanocluster depend to a great extent on the temperature. Density functional theory and nanothermodynamics can be combined to compute the geometrical optimization of isomers and their spectroscopic properties in an approximate manner. In this article, we investigate entropy-driven isomer distributions of Cu$_{38}$ clusters and the effect of temperature on their UV-visible and IR spectra. An extensive, systematic global search is performed on the potential and free energy surfaces of Cu38 using a two-stage strategy to identify the lowest-energy structure and its low-energy neighbors. The effects of temperature on the UV and IR spectra are considered via Boltzmann probability. The computed UV-visible and IR spectrum of each isomer is multiplied by its corresponding Boltzmann weight at finite temperature. Then, they are summed together to produce a final temperature-dependent, Boltzmann-weighted UV-visible and IR spectrum. Additionally, Molecular Dynamics simulation of the Cu$_{38}$ nanocluster was performed to gain insight into the system dynamics and make a three-dimensional movie of the system with atomistic resolution. Our results show the thermal populations at the absolute temperature of Cu38 cluster, and the disordered structure that dominates at high temperatures.

cond-mat.mtrl-sci↗