Dependency of XC functionals and role of 3s(2p) orbitals of Co(Si) as core/valence states on the vibrational and thermodynamic properties of CoSi

Abstract

Here, we investigate the effect of exchange correlation (XC) functionals and role of 3s(2p) orbitals of Co(Si) as core/valence states on the vibrational and thermodynamic properties of CoSi. Phonon calculations are carried out by finite displacement method with supercell approach using equilibrium crystal structures obtained from DFT calculations. Three XC functionals, viz. LDA, PBEsol and SCAN are employed. SCAN gives the highest phonon frequency of ~56 meV in good agreement with experiment, while LDA (PBEsol) gives ~54 (~55) meV. The zero-point energy is calculated as ~10 kJ/mol for all the functionals. The Debye temperatures are computed as ~626 K, ~638 K and ~650 K for LDA, PBEsol and SCAN, respectively. The phonon dispersion and phonon DOS are found to be dependent whether 3s(2p) orbitals of Co(Si) are considered as core or valence states. But, this orbital dependency is seemed to be insignificant on the thermal properties of this compound.