First-principles study of the phonon vibrational spectra and thermal properties of hexagonal MoS2

Abstract

The phonon spectra and thermal properties of the hexagonal MoS2 are investigated by using first-principles calculations within the density functional theory (DFT). Finite displacement method is used to calculate the phonon vibrational spectra and phonon density of states. The vibrational modes at the Gamma point are analyzed by using group theory. The temperature and pressure dependence of its thermal quantities such as the thermal expansion, the heat capacity at constant volume, the Gibbs energy and entropy are obtained based on the quasi-harmonic approximation (QHA). Our results show that both the thermal expansion coefficient α and the heat capacity CV increase with T3 at low temperatures and gradually turn almost linear as the temperature increases. It is found that the entropy is sensitive to the temperature while the Gibbs free energy is more sensitive to the pressure change.