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

TL;DR

This study examines how different exchange correlation functionals and the treatment of 3s(2p) orbitals as core or valence states influence the vibrational and thermodynamic properties of CoSi, using first-principles phonon calculations.

Contribution

It provides a comparative analysis of LDA, PBEsol, and SCAN functionals on phonon and thermal properties of CoSi, highlighting the orbital role's insignificance on thermal behavior.

Findings

SCAN yields phonon frequencies close to experimental values.

LDA provides the best agreement for Debye temperature.

Orbital treatment affects phonon dispersion but not thermal properties.

Abstract

First-principles phonon calculations along with density functional theory (DFT) play an important role to study the dynamical and thermal properties of materials. Here, we investigate the effect of exchange correlation (XC) functionals on the vibrational and thermodynamic properties of CoSi. The role of 3s(2p) orbitals of Co(Si) as core/valence states on the phonon properties of this compound is also studied. Phonon calculations are carried out by finite displacement method with supercell approach using equilibrium crystal structures obtained from DFT calculations. The calculated results are compared with the existing experiment. Three XC functionals, viz., LDA, PBEsol and SCAN are used for calculating the phonon dispersion, phonon density of states (DOS)/partial DOS and thermal properties of this compound. SCAN is found to give the highest phonon frequency of $\sim$56 meV which is in good agreement with the experimental value, while LDA (PBEsol) gives $\sim$54 ($\sim$55) meV. The zero-point energy is calculated as $\sim$ 10 kJ/mol for all the functionals. The Debye temperatures ($\Theta_{D}$) are computed as $\sim$626 K, $\sim$638 K and $\sim$650 K for LDA, PBEsol and SCAN, respectively. The $\Theta_{D}$ obtained from LDA gives the good agreement with the reported value. 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.