Abstract: Phonon dispersions,density of phonon states and thermodynamic property of cubic Ca2Si have been calculated by the Norm-Conserving method and Ultra Soft Pseudo-Potential method,respectively.The phonon dispersion and density phonon states of cubic Ca2Si have been confirmed by linear response method and finite displacement method.The result of phonon dispersion and density phonon states show that cubic phase was an unstable structure and the phonon vibration was anisotropic.The heat capacity,enthalpy,entropy and free energy were changed with temperature changing,and the Cv-T curve conformed to the Debye third power law in the low temperature condition.The heat capacity Cv =21 J ·mol-1 · K-1 at 1000 K,in the high temperature condition the CV→3R with the temperature increasing.The results of the study on the dispersion of phonon,phonon density and thermodynamic property were obtained that the oscillatory systems were formed with phonon and electron.

Key words: Phonon dispersions,density of phonon states and thermodynamic property of cubic Ca2Si have been calculated by the Norm-Conserving method and Ultra Soft Pseudo-Potential method,respectively.The phonon dispersion and density phonon states of cubic Ca2Si have been confirmed by linear response method and finite displacement method.The result of phonon dispersion and density phonon states show that cubic phase was an unstable structure and the phonon vibration was anisotropic.The heat capacity,enthalpy,entropy and free energy were changed with temperature changing,and the Cv-T curve conformed to the Debye third power law in the low temperature condition.The heat capacity Cv =21 J ·mol-1 · K-1 at 1000 K,in the high temperature condition the CV→3R with the temperature increasing.The results of the study on the dispersion of phonon,phonon density and thermodynamic property were obtained that the oscillatory systems were formed with phonon and electron.