Convex-Core Model of Molecules in Crystalline State

Abstract

The convex-core model of nonspherical molecules, introduced for the sake of treating the second virial coefficients of nonpolar gases (T. Kihara: Revs. Modern Phys. 25 (1953) 831), is applied to crystals of methane, carbon dioxide, and nitrogen. By use of model parameters determined from the second virial coefficients, lattice constants and cohesive energies are calculated. For methane, results of the calculations agree with observed values when the zero-point energy and the effect of potential non-additivity are taken into account. The crystal structure, the lattice constant and the cohesive energy of carbon dioxide are explained by use of a convex-core model with an embedded electric quadrupole.