By Wei Wu
The State Key Laboratory of Physical Chemistry of Solid Surfaces, iChEM, Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry
& College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, Fujian 361005, China

A hierarchy of valence bond (VB) methods based on the concept of seniority number, defined as the number of singly occupied orbitals in a determinant or an orbital configuration, will be presented in this talk. It is found from several test examples that the seniority-based VB expansion converges more rapidly toward the full configuration interaction (FCI) or complete active space self-consistent field (CASSCF) limit and produces more accurate PECs with smaller non-parallelity errors than its molecular orbital (MO) theory based analogue.