EXTREMAL ELECTRON PAIRS

Extremal pair functions for an n-electron wave function of a closed-sh ell state are defined as linear combinations of spin-orbital-product p air functions that make some functionals (e.g., r(12)(2) or r(12)(-1)) extremal. They are related to the natural spin geminals in the uncorr elated limit and are useful both for an analysis of wave functions in view of an understanding of the chemical bond and for the treatment of electron correlation. Numerical examples are shown and discussed for He-2 as well as the 10-electron systems Ne, HF, H2O, NH3, and CH4. (C) 1996 John Wiley & Sons, Inc.