Investigation of thermophysical, electronic and lattice dynamic properties for CaX2Si2 (X=Ni,Zn,Cu,Ag,Au) via first-principles calculations

Abstract

Abstract The thermophysical and electronic properties as well as the lattice dynamics of ThCr2Si2-type CaX2Si2 (X = Ni, Zn, Cu, Ag, Au) are investigated by using first-principles calculations based on the density functional theory (DFT). The lattice constants and formation enthalpies of CaX2Si2 are elaborately calculated. All of calculated results are in good agreement with the experimental data. The mechanical properties, including single crystal elastic constants, polycrystalline elastic moduli and orientation dependence of Young’s moduli and shear moduli of CaX2Si2, and electronic properties such as the electronic density of states (DOS) and charge density distribution of CaX2Si2 are predicted in this work. The calculated charge density indicates the presence of covalent bonding between Si–Si atoms in CaX2Si2 compounds. The calculations of phonon spectrum and phonon density of states for CaX2Si2 are also completed. The imaginary frequency of CaZn2Si2 in the vicinity of Γ point indicates that the CaZn2Si2 phase is dynamically instable at the ground state. Based on the phonon spectrum calculation, the predictions of heat capacity and entropy for CaX2Si2 are accomplished with quasi-harmonic approximation.