Projected seniority-two orbital optimization of the antisymmetric product of one-reference orbital geminal

K. Boguslawski, P. Tecmer, P.A. Limacher, P.A. Johnson, P.W. Ayers, P. Bultinck, S. De Baerdemacker, D. Van Neck
Journal of Chemical Physics
140 (21), 214114
2014
A1

Abstract 

We present a new, non-variational orbital-optimization scheme for the antisymmetric product of one-reference orbital geminal wave function. Our approach is motivated by the observation that an orbital-optimized seniority-zero configuration interaction (CI) expansion yields similar results to an orbital-optimized seniority-zero-plus-two CI expansion [L. Bytautas, T. M. Henderson, C. A. Jimenez-Hoyos, J. K. Ellis, and G. E. Scuseria, J. Chem. Phys. 135, 044119 (2011)]. A numerical analysis is performed for the C-2 and LiF molecules, for the CH2 singlet diradical as well as for the symmetric stretching of hypothetical (linear) hydrogen chains. For these test cases, the proposed orbital-optimization protocol yields similar results to its variational orbital optimization counterpart, but prevents symmetry-breaking of molecular orbitals in most cases. (C) 2014 AIP Publishing LLC.