title: Nonvariational Orbital Optimization Techniques for the AP1roG Wave Function.
abstract: We introduce new nonvariational orbital optimization schemes for the antisymmetric product of one-reference orbital geminal (AP1roG) wave function (also known as pair-coupled cluster doubles) that are extensions to our recently proposed projected seniority-two (PS2-AP1roG) orbital optimization method [ J. Chem. Phys. 2014 , 140 , 214114 )]. These approaches represent less stringent approximations to the PS2-AP1roG ansatz and prove to be more robust approximations to the variational orbital optimization scheme than PS2-AP1roG. The performance of the proposed orbital optimization techniques is illustrated for a number of well-known multireference problems: the insertion of Be into H2, the automerization process of cyclobutadiene, the stability of the monocyclic form of pyridyne, and the aromatic stability of benzene.
authors.affiliation: Department of Chemistry and Chemical Biology, McMaster University , 1280 Main Street West, Hamilton, L8S 4M1 Ontario, Canada.
authors.forename: Katharina
authors.initials: K
authors.lastname: Boguslawski
authors.affiliation: Department of Chemistry and Chemical Biology, McMaster University , 1280 Main Street West, Hamilton, L8S 4M1 Ontario, Canada.
authors.forename: Paweł
authors.initials: P
authors.lastname: Tecmer
authors.affiliation: Department of Inorganic and Physical Chemistry, Ghent University , Krijgslaan 281 (S3), 9000 Gent, East Flanders, Belgium.
authors.forename: Patrick
authors.initials: P
authors.lastname: Bultinck
authors.affiliation: Center for Molecular Modelling, Ghent University , Technologiepark 903, 9052 Gent, East Flanders, Belgium.
authors.forename: Stijn
authors.initials: S
authors.lastname: De Baerdemacker
authors.affiliation: Center for Molecular Modelling, Ghent University , Technologiepark 903, 9052 Gent, East Flanders, Belgium.
authors.forename: Dimitri
authors.initials: D
authors.lastname: Van Neck
authors.affiliation: Department of Chemistry and Chemical Biology, McMaster University , 1280 Main Street West, Hamilton, L8S 4M1 Ontario, Canada.
authors.forename: Paul W
authors.initials: PW
authors.lastname: Ayers