Estudio Ab initio de las propiedades estructurales, electrónicas y magnéticas del AlAs dopado con cobalto, níquel o carbono

Las propiedades magnéticas del compuesto CoxAl1-xAs (NixAl1-xAs) es una consecuencia directa de la presencia de Co (Ni) en su estructura, el cual aporta casi la totalidad de la magnetización. El estado fundamental ferromagnético del CoxAl1-xAs se origina en la fuerte hibridación entre los estados 3d-Co y 4p-As. Por otro lado, el antiferromagnetismo en el NixAl1-xAs se genera debido a que el acoplamiento entre los estados 3d-Ni y 4p-As es muy débil, causando que una de las impurezas de Ni y su ambiente químico se magneticen en una dirección, mientras que la otra se magnetiza en dirección contraria; mediante el apareamiento promedio de espín por interacción dipolo-dipolo característico del efecto de superintercambio. El compuesto CxAlAs1-x no presenta un comportamiento magnético. Los cálculos de la estructura electrónica revelan que el dopaje con C provoca un comportamiento metálico debido a la presencia de los estados electrónicos p del Al, As y C alrededor del nivel de Fermi

Structural, elastic, electronic and thermal properties of InAs: A study of functional density

In this research, first-principles calculations were carried out within the density functional theory (DFT) framework, using LDA and GGA, in order to study the structural, elastic, electronic and thermal properties of InAs in the zinc-blende structure. The results of the structural properties (a, B0, ) agree with the theoretical and experimental results reported by other authors. Additionally, the elastic properties, the elastic constants (C11, C12 and C44), the anisotropy coefficient (A) and the predicted speeds of the sound ( , , and ) are in agreement with the results reported by other authors. In contrast, the shear modulus (G), the Young's modulus (Y) and the Poisson's ratio (v) show some discrepancy with respect to the experimental values, although, the values obtained are reasonable. On the other hand, it is evident the tendency of the LDA and GGA approaches to underestimate the value of the band-gap energy in semiconductors. The thermal properties (V, , θD yCV) of InAs, calculated using the quasi-harmonic Debye model, are slightly sensitive as the temperature increases. According to the stability criteria and the negative value of the enthalpy of formation, InAs is mechanically and thermodynamically stable. Therefore, this work can be used as a future reference for theoretical and experimental studies based on InAs

Exploring DFT+U parameter space with a Bayesian calibration assisted by Markov chain Monte Carlo sampling

The density-functional theory is widely used to predict the physical properties of materials. However, it usually fails for strongly correlated materials. A popular solution is to use the Hubbard correction to treat strongly correlated electronic states. Unfortunately, the values of the Hubbard U and J parameters are initially unknown, and they can vary from one material to another. In this semi-empirical study, we explore the U and J parameter space of a group of iron-based compounds to simultaneously improve the prediction of physical properties (volume, magnetic moment, and bandgap). We used a Bayesian calibration assisted by Markov chain Monte Carlo sampling for three different exchange-correlation functionals (LDA, PBE, and PBEsol). We found that LDA requires the largest U correction. PBE has the smallest standard deviation and its U and J parameters are the most transferable to other iron-based compounds. Lastly, PBE predicts lattice parameters reasonably well without the Hubbard correction

Exploring the elastic and electronic properties of chromium molybdenum diboride alloys

We perform first-principles calculations to study the structural, mechanical, thermal, electronic, and magnetic properties of CrMoB for x = 0.25, 0.33, 0.50, 0.67 and 0.75. Based on structural search methods, we determine the ground-state structure for each concentration. The ternaries are either monoclinic (x = 0.25, 0.75) or trigonal (x = 0.33, 0.50, 0.67). The calculated mechanical properties reveal that the strength of CrMoB is maximized for x = 0.50. CrMoB exhibits excellent mechanical properties (B = 298 GPa, Y = 558 GPa, G = 235 Gpa, ν = 0.19, H =27 GPa), surpassing those of β-MoB at a lower cost. All of these ternaries are hard alloys with Vickers hardness greater than 24 GPa. Chemical bonding analysis demonstrates that the strength of the new compounds is related to the alternating planar and buckled B-B layers, as well as the strong TM-B bonds. The enhanced strength of CrMoB is a consequence of the high density of strong interlayer Cr-Mo metallic bonds around the Fermi level.This work used the XSEDE which is supported by the USA National Science Foundation (NSF) grant number ACI-1053575. The authors also acknowledge the support from the Texas Advances Computer Center (with the Stampede2 and Bridges supercomputers). We also acknowledge the use of the Super Computing System (Thorny Flat) at WVU, which is funded in part by the NSF Major Research Instrumentation Program (MRI) Award #1726534. This work was supported by the DMREF-NSF 1434897, NSF OAC-1740111 and DOE DE-SC0021375 projects

Structural, elastic, electronic and thermal properties of InAs: A study of functional density

In this research, first-principles calculations were carried out within the density functional theory (DFT) framework, using LDA and GGA, in order to study the structural, elastic, electronic and thermal properties of InAs in the zinc-blende structure. The results of the structural properties (a, B0, ) agree with the theoretical and experimental results reported by other authors. Additionally, the elastic properties, the elastic constants (C11, C12 and C44), the anisotropy coefficient (A) and the predicted speeds of the sound ( , , and ) are in agreement with the results reported by other authors. In contrast, the shear modulus (G), the Young's modulus (Y) and the Poisson's ratio (v) show some discrepancy with respect to the experimental values, although, the values obtained are reasonable. On the other hand, it is evident the tendency of the LDA and GGA approaches to underestimate the value of the band-gap energy in semiconductors. The thermal properties (V, , θD yCV) of InAs, calculated using the quasi-harmonic Debye model, are slightly sensitive as the temperature increases. According to the stability criteria and the negative value of the enthalpy of formation, InAs is mechanically and thermodynamically stable. Therefore, this work can be used as a future reference for theoretical and experimental studies based on InAs.En esta investigación se realizaron cálculos de primeros principios en el marco de la teoría del funcional de la densidad (DFT), utilizando las aproximaciones LDA y GGA, con el fin de estudiar las propiedades estructurales, elásticas, electrónicas y térmicas del InAs en la estructura zinc blenda. Los resultados de las propiedades estructurales (a, B0, ) muestran un buen acuerdo con los resultados teóricos y experimentales reportados por otros autores. Con respecto a las propiedades elásticas, las constates elásticas (C11, C12 y C44), el coeficiente de anisotropía (A) y las velocidades del sonido ( ,  y ) predichas están acordes con los resultados reportados por otros autores. En contraste, el módulo de Shear (G), el módulo de Young (Y) y la razón de Poisson (v) presentan cierta discrepancia con respecto a los valores experimentales; sin embargo, los valores obtenidos son razonables. Por otro lado, se evidencia la tendencia de las aproximaciones LDA y GGA a subestimar el valor de la brecha de energía prohibida en los semiconductores. Las propiedades térmicas (V, , θD yCV) del InAs, calculadas usando el modelo cuasi-armónico de Debye, son ligeramente sensibles a medida que aumenta la temperatura. De acuerdo con los criterios de estabilidad y el valor negativo de la entalpia de formación, el InAs es mecánicamente y termodinámicamente estable. Por lo tanto, este trabajo puede ser utilizado como referencia para estudios teóricos y experimentales basados en InAs