Theoretical study of the thermochemistry of sulfur molecular crystals.: I.: Method and application to α- and 1D-polymerized sulfurs

The combination of two semiempirical methods, the "extended Huckel theory" for repulsive energy and a method derived from classical perturbation expansions for the dispersion energy, is used to evaluate the weak interaction energy between covalent rings or chains of sulfur compounds. In this paper, the parametrization method of both parts of the energy is set up. The volume of the elementary cell and the heat of sublimation of cr-sulfur are in correct agreement with experimental values. As a test for the study of polymerized omega-sulfur, a simple 1D-example shows correct behavior for interchain distance and cohesive energy. In each case,a detailed analysis of the contribution of each term involved in the total intermolecular potential function is given. In particular, we show the importance of three-body terms in the energetics of such structures.