COMBINING AB-INITIO TECHNIQUES WITH ANALYTICAL POTENTIAL FUNCTIONS FOR STRUCTURE PREDICTIONS OF LARGE SYSTEMS - METHOD AND APPLICATION TO CRYSTALLINE SILICA POLYMORPHS

A computational scheme is presented which combines quantum mechanical ab initio techniques with methods using analytical potential functions . The scheme is designed for use in structure optimizations and is als o applicable to molecular dynamics simulations. The implementation cov ers both molecular and periodic systems. The problem of the link atoms is solved by a subtraction scheme which is easily implemented for any combination of methods. As a first application dense and microporous silica polymorphs are studied. The Hartree-Fock method is combined wit h both a force field and an ion pair shell model potential. Comparison is made with lattice energy minimizations which use the force field o r the shell model potential alone as well as with free cluster optimiz ations and optimizations in which the outer part of the cluster is kep t fixed. (C) 1997 by John Wiley & Sons, Inc.