Evaluation of the charge penetration energy between non-orthogonal molecular orbitals using the Spherical Gaussian Overlap approximation

An overlap dependent formula for evaluating the charge penetration energy b etween non-orthogonal molecular orbitals is derived using the Spherical Gau ssian Overlap approximation. When combined with an accurate multipole repre sentation of the electrostatic energy, such as in the effective fragment po tential method, ab initio electrostatic energies are generally reproduced t o within 0.2 kcal/mol for a variety of molecular dimers and basis sets. The only larger error is for the DMSO dimer, where the electrostatic energy is overestimated by 0.7 kcal/mol. (C) 1999 Elsevier Science B.V. All rights r eserved.