ANALYTIC EQUATION OF STATE AND THERMODYNAMIC PROPERTIES FOR FCC C₇₀ SOLID BASED ON THE ANALYTIC MEAN FIELD APPROACH

The analytic expressions for equation of state and internal energy for the poly-exponential solid have been derived based on the analytic mean-field potential (AMFP) method. The formalism is applied to the fcc C 70 solid. One set of potential parameters are determined through fitting the experimental compression data1 of C 70 up to 1 GPa and at temperature 365 K. The difference between the well depth for C 70 molecules and that for C 60 molecules is fairly small. The thermo-physical properties including the isothermals, thermal expansivity, isochoric heat capacity, Helmholtz free energy and internal energy have been calculated and analyzed. The theoretical results are in good agreement with the experimental data of C 70 solid available. Based on the results of our calculations, we may also predict the behaviors of C 70 at extreme conditions.