Ab initio group model potentials including electron correlation effects

A method for determination of ab initio group model potentials, with the in tention of describing the effects of a whole molecule or a chemical group w ithin a density functional theory framework, is reported. The one-electron part of the Kohn-Sham equations is modified by incorporation of a Coulomb o perator, which accounts for the classical electron interaction arising from the group. Exchange and correlation effects are introduced by a suitable m odification of the exchange-correlation functionals. The strong orthogonali ty condition, usually required by the theory of separability of many electr on systems, is written in terms of first order reduced density matrices. In order to check the method a group model potential for H2O (environment) wa s obtained and employed in the calculation of HF ... H2O and H2O ... H2O co mplexes using several functionals. Equilibrium intergroup distances and bin ding energies are compared with all-electron calculations. (C) 2000 America n Institute of Physics. [S0021-9606(00)30337-3].