Bulk properties of C76 and C84 fullerites studied by MD simulation based on a central two body intermolecular potential

Molecular dynamics simulations based on the Girifalco central two-body potential are performed in order to study bulk properties of solid C-76 and C-84. The fullerene cages are modelled as rigid sphere whose 'effective' diameter is first determined in such a way that NVT-NPT simulations of the model fullerite reproduce the experimental lattice constant at ambient pressure and at various temperatures. It turns out that the diameter so fixed depends only slightly on the temperature. A unique molecular size, yielding the fit of the lattice constant at a conveniently chosen temperature, is then adopted throughout the whole temperature ranges investigated; the lattice constants, and the internal potential energy of C-76 and C-84 thereby calculated at various T, turn out to be in qualitative agreement with the available experimental data. The equation of state at ambient temperature is then also calculated. Results for C-76 compare favorably with experiment only at low pressures; by converse, results for C-84 turn out to be qualitatively or semi-quantitatively accurate up to 9 GPa. Other possible applications of the model are discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.