EFFECT OF OVERLAP ON SEMIEMPIRICAL POTENTIALS DERIVED FROM TIGHT-BINDING

Overlap must explicitly be included when empirical interatomic potenti als for use in environments of low symmetry are derived using tight-bi nding theory. We derive a simplified real-space total-energy expressio n that takes into account the first and second moments of the density of states including overlap. It uses the extended Huckel theory and Ta ylor and Pade truncations for the inverse of the overlap matrix. Our a pproximate expression is tested for an s-band nearest-neighbor model b y carrying out numerical integrations over exact densities of states f or many lattices of different dimensionality and coordination number. Within a two-body simplification the inclusion of overlap leads to a n ew functional form for use in developing embedded-atom functionals. Qu antitative accuracy is improved, however, when the three-body Pade-app roximation-derived form is used.