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 large molecules. This method uses pseudo-Hartree-Fock (P-HF) molecular orbitals formed from HF atomic orbitals but without Fock matrix diagonalization. The occupied P-HF orbitals are projected onto atomic basis functions to obtain GVB first natural orbitals, and the unoccupied HF orbitals are projected to obtain GVB second natural orbitals. This method (denoted GVB-INIT) is fast because no HF wave functions need be calculated and because the localization is piecewise atomic. In conjunction with the recently developed GVB-DIIS method for converging GVB wave functions and the new pseudospectral programs (PS-GVB) for the Fock matrix 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.
© 1994 American Chemical Society. Received: June 20, 1994; In Final Form: October 4, 1994. This research was partially funded by the National Science Foundation (Che 91-100284 and ASC 92-17368). The facilities at the MSC/BI are also supported by grants from DOE-AICD, Allied-Signal Corp., Asahi Chemical, Asahi Glass, BP America, Chevron Petroleum Technology Co., B.F. Goodrich, Teijin Ltd., Hughes Research Labs., Xerox Corp., and Beckman Institute. Some of these calculations were carried out on the NSF Pittsburgh Supercomputing Center and some on the JPL Cray YMP.