Extension of the Gordon–Kim overlap interaction to open shell systems

Abstract

An attempt is made to extend the theory of interatomic interactions for closed shell systems to bonded solids by proceeding in two steps. In the first step, the states are restricted to prevent the formation of bonds and the Gordon–Kim approach is used. In the second step, the change in energy due to bond formation is estimated using the bond orbital model and parameters obtained from the optical reflectivity peak. Calculated bond lengths, cohesive energies, and bulk moduli for diamond, silicon, and germanium show correct trends and semiquantitative agreement with experiment in most values, but considerably less accuracy than that obtained for closed-shell systems. Consideration of the various contributions suggests that the discrepancies arise from the use of free-electron exchange and free-electron kinetic energy for a system (in step one) which is not in the ground state.