The Generalized Multiconfiguration Spin-Coupled Method, STO optimization, and the Electronic Structure of BH3 in its ground state

The Optimized Basis Set - Generalized Multiconfiguration Spin-Coupled method, or OBS-GMCSC for short, offers a practical approach to the direct variational calculation of non-orthogonal multiconfiguration electronic wavefunctions. Simultaneous optimization of STO exponential parameters enables high accuracy with rather small basis sets and ensures strict compliance with the virial theorem. OBS-GMCSC wavefunctions can yield compact and accurate descriptions of atomic and molecular electronic structures, and neatly resolve symmetry-breaking difficulties, as illustrated by a brief review of previous results for the boron anion and the dilithium molecule, and by newly obtained results for BH3.