MODIFICATION OF THE LOCAL SELF-CONSISTENT-FIELD METHOD FOR MODELING SURFACE REACTIVITY OF COVALENT SOLIDS

The local self-consistent field (LSCF) method which allows full SCF co mputations on a fragment of very long molecular systems represented by a classical force field has been adapted to the description of nonmet allic crystals. The periodicity of the network is achieved by modifyin g self-consistently the basic parameters of the classical subsystem (c harges, geometric parameters) along the SCF iterative scheme. The meth od is tested on cr-cristobalite. The parametrization of the quantum cl assical junction, achieved by localized bond orbitals has been perform ed with the help of a fragment located in the bulk. The stability of t he method with respect to the size of the fragment and the size of the crystalline sample appears to be very good. The properties of fully h ydroxylated (010) surface are corrected described. Modeling of water a dsorption on the ideal surface as well as on two kinds of surface defe cts gives rise to very reasonable results with an absorption energies of ca 10 kcal/mol which are close to the upper limit of the experiment al data. This preliminary study appears to be quite encouraging regard ing the possibilities of using this method, which can be considered as an extension of the embedded cluster approach to covalent solids. Man y applications to surface chemical reactivity studies can be imagined. (C) 1996 John Wiley & Sons, Inc.