CALCULATIONS OF THE THERMAL-EXPANSION, COHESIVE ENERGY AND THERMODYNAMIC STABILITY OF A VAN-DER-WAALS CRYSTAL - FULLERENE C-60

The temperature dependence of the intermolecular distance and the cohesive energy in the high-temperature modification of C-60 solid fullerene was studied on basis of the correlative method of unsymmetrized self-consistent field. The central intermolec ular potential of Girifalco and its approximation by Yakub were used. We conclude about the decisive role of anharmonic effects at high temperatures. The discrepancy between the calculated and experimental values of intermolecular distance does not exceed 0.8% on the whole temperature interval. The temperature of loss of thermodynamic stability was obtained (approximate to 1915 K) and a possible melting temperature was estimated (approximate to 1400 K).