QUANTUM-CHEMICAL COMPUTATIONS ON PARTS OF LARGE MOLECULES - THE AB-INITIO LOCAL SELF-CONSISTENT-FIELD METHOD

In this Letter we extend to the ab initio level the principles of the local self consistent field method (LSCF) developed earlier within the semiempirical approximations. It allows quantum electronic computatio ns on a fragment of a large molecule mostly depicted by a classical fo rce field, The bond separating the quantum subsystem from the classica l one is assumed to be represented by localized orbitals introduced as data. The molecular orbitals of this subsystem are developed on a bas is of functions, orthogonal to the localized orbitals, which derive fr om the atomic orbitals of the usual basis set by a simple linear trans formation. The algorithm of the LSCF method is obtained by a simple mo dification of the standard Hartree-Fock or DFT codes.