GENERALIZATION OF THE OPTIMIZED-BASIS-SET MULTI-CONFIGURATION SPIN-COUPLED METHOD FOR THE AB INITIO CALCULATION OF ATOMIC AND MOLECULAR ELECTRONIC WAVE FUNCTIONS

摘要

An ab initio procedure for the calculation of atomic and molecular electronic wave functions, the Optimized-Basis-Set Multi-Configuration Spin-Coupled (OBS-MCSC) method, is generalized by introducing a separate linear combination of spin functions for each configuration, turning it into the OBS-GMCSC method. The ability to use a second-order minimization procedure in the computation of the wave function is maintained through appropriate generalization of the analytic expressions for the first and second derivatives of the energy with respect to the optimization parameters, as is the optional inclusion among the latter of the basis-function exponential parameters. The generalization, a variational improvement of the wave function, strengthens the connection with classical VB theory, of which the method can now be considered an optimized-orbitals variant, while maintaining the link with single-configuration Spin-Coupled theory, of which it may still be considered a multiconfiguration extension. The method can also be viewed as a nonorthogonal variant of the MCSCF approach. To demonstrate its practical feasibility and usefulness, the OBS-GMCSC method is applied to a study of the electronic structure and electron affinity of boron. (C) 1996 John Wiley & Sons, Inc. [References: 22]