Lattice dynamics, thermal expansion and specific heat of a Lennard-Jones solid in the quasi-harmonic approximation

Abstract

In this paper we present the results of an ab initio calculation of the thermal expansion, the specific heat and the mean-square amplitude of vibration of a Lennard-Jones crystal, carried out in the quasi-harmonic approximation. The dynamical problem is solved for 110 values of the density, and the thermal expansion is obtained from a proper minimization of the Helmholtz free energy F(T, a) (2a is the lattice constant). Particular attention is given to the strong density dependence of the vibrational frequencies and the resultant effects on the thermodynamic quantities.