  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.
