THEORETICAL-STUDY OF THE THERMOCHEMISTRY OF SULFUR MOLECULAR-CRYSTALS- I - METHOD AND APPLICATION TO ALPHA-POLYMERIZED AND 1D-POLYMERIZED SULFURS

The combination of two semiempirical methods, the ''extended Huckel th eory'' for repulsive energy and a method derived from classical pertur bation expansions for the dispersion energy, is used to evaluate the w eak interaction energy between covalent rings or chains of sulfur comp ounds. 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 su blimation of cr-sulfur are in correct agreement with experimental valu es. As a test for the study of polymerized omega-sulfur, a simple 1D-e xample shows correct behavior for interchain distance and cohesive ene rgy. 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 energeti cs of such structures.