APPLICATION OF A SPHERICALLY AVERAGED POTENTIAL TO SOLID C70 IN THE DISORDERED PHASE

A spherically averaged potential was used to calculate solid state properties for C{sub 70} in the disordered fcc phase. Each molecule was treated as a spherical shell of 70 carbons with radius of 3.8 A, determined by fitting the equation of state to the experimental X-ray powder diffraction data. The anharmonic properties were treated by using the extended Mie-Gruneisen theory. This approach enabled us to compute compressibility and thermal expansion as well as the phase transition point between the solid and the vapor phases of C{sub 70}. The calculated enthalpy of sublimation, 193 kJ/mol, lies within the range of measured heats, while the predicted sublimation point of 1023 K is higher than the experimentally determined one. 13 refs., 3 figs., 1 tab.