Weyl semimetal (WSM) is a new type of topological quantum material for future spintronic devices. Using the first-principles density functional theory, we systematically investigated the thermal expansion properties, and the temperature dependence of isovolume heat capacity and bulk modulus in WSMs MX (M = Nb, Ta; X = P, As). We also presented the phonon dispersion curves and its variation under stress in MX and the anisotropic thermal expansion properties due to the anisotropic crystal structure in WSMs have been predicted in our calculations. Intriguing, we found that the heat capacities increase more rapidly with increasing temperature in the low temperature region for all MX. Furthermore, our results showed that the thermal expansion properties are determined mainly by the isovolume heat capacity at low temperatures, while the bulk modulus has the major effect at high temperatures. These results are useful for applications of WSMs in electronic and spintronic devices.

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Employing first-principles combined with hybrid functional calculations, the electronic and optical properties of GaAs alloyed with isovalent impurities Bi and N are investigated. As GaAsBiN alloy is a quaternary alloy, the band gap and the lattice constant of the alloy can be individually tuned. Both impurities are important to the valence band and conduction band of the alloy, with the band gap of the alloy being dramatically reduced by Bi 6p states and N localized 2s states. Interestingly, the calculated optical properties of the quaternary alloy are similar to those of undoped GaAs except that the absorption edge has a redshift toward lower energy. These results suggest potential interest in the long-wavelength applications of GaAsBiN alloy.

By using molecular dynamics method, transition of Al-Co alloy from liquid to amorphous structure has been investigated theoretically. The structure parameters, pair distribution functions (PDF), bond-angle distribution functions, and Voronoi polyhedra analysis are adopted as indicators of the evolution of clusters in Al-Co alloy during the rapid cooling processes. We found that below transition temperature, the second peak of PDF curves splits into two pronounced subpeaks, while at all temperature the PDF curves gradually converge to unity at large distance. This indicates that the amorphous alloy exhibits local ordering structure and has no long-range ordering. Besides, the bond-angle distribution function predicts that the degrees in the vicinity of 63.4 and 113.4 are dominated in the system during the processes of rapid annealing, which represent that the icosahedral structures are dominant. Together with the cluster structures observed in simulation, Voronoi polyhedra analysis shows that the most popular polyhedron is full icosahedron with the Voronoi index 〈0, 0, 12, 0〉, which is always predominant in bulk metallic glass (MG) formers with excellent glass forming ability. Our studies indicated that doping of cobalt atoms in the Al-based alloy should have a better capacity of forming MG.