Cluster integrals of convex molecule systems

Cluster integrals assigned to particles interacting via the Kihara non-sphe rical potential are studied theoretically. An exact formula is derived whic h allows one to consider the effect of molecular shape separately from the effect of soft interactions. Employing the proposed formalism, the cluster integrals are analysed. The approach is applied to determine the third viri al coefficient and an efficient computational method is developed. The thir d virial coefficient was calculated for a combination of molecules with har d cores of prolate spherocylindrical- and spherical shapes interacting via the square-well, triangle-well and 12-6 pair potentials. Comparison with nu merical results obtained by Monte Carlo integration is made and fair agreem ent is found.