Basis set and correlation effects in configuration analysis of reactive systems

A methodology for the configuration analysis of multi-configurational wave- functions of a closed-shell system is presented. The molecular system is pa rtitioned in interacting fragments, the molecular orbitals are expanded in fragment orbitals and each Slater determinant is expanded in localized reac tant electronic structures. Finally, to reduce the number of relevant coeff icients, a transformation of orbitals is performed. The main advantage of e mploying configuration analysis lays in its simplicity and compactness, spe cially when extended basis sets are used. As a test, the wave-function at t he transition state for some nucleophilic substitution reactions is analyze d. (C) 2000 Elsevier Science B.V. All rights reserved.