A new separable potential operator for representing a chemical bond and other applications

A new type of potential operator has several kinds of applications in elect ronic structure calculations. Three uses are envisaged here. First when som e special region of a covalently bonded solid or very large molecule is mod eled by a modest sized cluster, each dangling bond at the cluster surface c an be saturated in a way that exactly reproduces the bond in the complete s ystem. Second a similar approach can be used at the matching surface in an embedding scheme for calculations on the same type of systems. The third ap plication is to atomic pseudopotentials where the new potential operator av oids the possibility of "ghost" states that sometimes plague the widely use d Kleinman-Bylander form of the pseudopotential. The theory of the new sepa rable potential and its application to the dangling bond problem are the ma in subjects of the present paper. Starting from a given potential or pseudo potential, the new separable operator modifies some of the required eigenfu nctions and eigenvalues in a controlled way while conserving all other eige nvalues. The method has been tested on the molecules X-SiH3 where X=H, F, C l, Br, or I. (C) 2001 American Institute of Physics.