title: Projected quasiparticle theory for molecular electronic structure.
abstract: We derive and implement symmetry-projected Hartree-Fock-Bogoliubov (HFB) equations and apply them to the molecular electronic structure problem. All symmetries (particle number, spin, spatial, and complex conjugation) are deliberately broken and restored in a self-consistent variation-after-projection approach. We show that the resulting method yields a comprehensive black-box treatment of static correlations with effective one-electron (mean-field) computational cost. The ensuing wave function is of multireference character and permeates the entire Hilbert space of the problem. The energy expression is different from regular HFB theory but remains a functional of an independent quasiparticle density matrix. All reduced density matrices are expressible as an integration of transition density matrices over a gauge grid. We present several proof-of-principle examples demonstrating the compelling power of projected quasiparticle theory for quantum chemistry.
authors.affiliation: Department of Chemistry, Rice University, Houston, Texas 77005, USA.
authors.forename: Gustavo E
authors.initials: GE
authors.lastname: Scuseria
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Jiménez-Hoyos
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Henderson
authors.forename: Kousik
authors.initials: K
authors.lastname: Samanta
authors.forename: Jason K
authors.initials: JK
authors.lastname: Ellis