Projected seniority-two orbital optimization of the Antisymmetric Product of one-reference orbital Geminal

摘要

We present a new, non-variational orbital-optimization scheme for theAntisymmetric Product of one-reference orbital Geminal wave function. Ourapproach is motivated by the observation that an orbital-optimizedseniority-zero configuration interaction (CI) expansion yields similar resultsto an orbital-optimized seniority-zero-plus-two CI expansion [J. Chem. Phys.,135, 044119 (2011)]. A numerical analysis is performed for the C$_2$, LiF andCH$_2$ molecules as well as for the symmetric stretching of hypothetical(linear) hydrogen chains. For these test cases, the proposedorbital-optimization protocol yields similar results to its variational orbitaloptimization counterpart, but prevents symmetry-breaking of molecular orbitalsin most cases.