RULE-BASED TRIAL WAVE-FUNCTIONS FOR GENERALIZED VALENCE-BOND THEORY

We present a general method suitable for automatic generation of trial wave functions for generalized valence bond (GVB) descriptions of lar ge molecules. This method uses pseudo-Haruee-Fock (P-HF) molecular orb itals formed from HF atomic orbitals but without Fock matrix diagonali zation. The occupied P-HF orbitals are projected onto atomic basis fun ctions to obtain GVB first natural orbitals, and the unoccupied HF orb itals are projected to obtain GVB second natural orbitals. This method (denoted GVB-INIT) is fast because no HF wave functions need be calcu lated and because the localization is piecewise atomic. In conjunction with the recently developed GVB-DIIS method for converging GVB wave f unctions and the new pseudospectral programs (PS-GVB) for the Fock mat rix elements, GVB-INIT makes calculation of highly correlated GVB wave functions quite practical. The efficacy of GVB-INIT is illustrated by application to several cases including GVB wave functions with up to 26 correlated pairs.