The second Grüneisen constant of CsCl and CsI

The first order volume dependence of the Grüneisen constant, commonly known as the second Grüneisen constant, has been obtained in a quasi-harmonic approximation as a function of temperature for CsCl and CsI. The calculations are performed using a volume dependent modified rigid ion model of lattice dynamics. The variation of the microscopic second mode-Grüneisen parameter as a function of wave vector in various directions of high symmetry is also calculated. The theoretically calculated second Grüneisen constants are compared to the values calculated using available thermodynamic data.