Electronic properties, anisotropic elasticity, theoretical strengths, and lattice vibrational mode of orthorhombic YSi

Abstract

We investigated the crystal structure, electronic structure, elastic stiffness constants, responses to tensile and shear deformations, lattice vibrational modes as well as vibration heat capacity and vibration entropy of the orthorhombic YSi compound using ab initio approach. The relaxed ground-state lattice constants a, b and c of YSi exhibit fair agreement with the available experimental and theoretical data. Nine independent elastic stiffness constants have been computed by increasingly varying minute strains based on “energy-strain” approach, which confirm that the orthorhombic YSi is mechanically stable. Some polycrystalline moduli involving bulk modulus, Young's modulus and shear modulus, Poisson's ratio, brittle/ductile characteristic have also been systematically derived, and YSi can be classified as brittle compound. Both three-directional Young's modulus anisotropy and bulk modulus anisotropy are calculated in detail, and the calculations indicate that the orthorhombic YSi takes on significant elastic anisotropy. We further studied the theoretical tensile and shear strengths under different loads. Also, the phonon spectra, total and partial phonon densities of states are researched by employing Density Functional Perturbation Theory (DFPT) and the finite-displacement method, and the infrared-active and Raman active vibration modes at the center of Brillouin zone are classified using the group theory. Moreover, we predicted the constant volume heat capacity of YSi under high temperature relying on the calculated phonon densities of states as well as quasi-harmonic approximation (QHA) and Debye model.