title: Analytic energy gradient for the projected Hartree-Fock method.
abstract: We derive and implement the analytic energy gradient for the symmetry Projected Hartree-Fock (PHF) method avoiding the solution of coupled-perturbed HF-like equations, as in the regular unprojected method. Our formalism therefore has mean-field computational scaling and cost, despite the elaborate multi-reference character of the PHF wave function. As benchmark examples, we here apply our gradient implementation to the ortho-, meta-, and para-benzyne biradicals, and discuss their equilibrium geometries and vibrational frequencies.
authors.affiliation: Department of Chemistry, Rice University, Houston, Texas 77251-1892, USA.
authors.forename: Roman
authors.initials: R
authors.lastname: Schutski
authors.affiliation: Department of Chemistry, Rice University, Houston, Texas 77251-1892, USA.
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Jiménez-Hoyos
authors.affiliation: Department of Chemistry and Department of Physics and Astronomy, Rice University, Houston, Texas 77251-1892, USA.
authors.forename: Gustavo E
authors.initials: GE
authors.lastname: Scuseria