Schutski, RomanJiménez-Hoyos, Carlos A.Scuseria, Gustavo E.2017-05-242017-05-242014Schutski, Roman, Jiménez-Hoyos, Carlos A. and Scuseria, Gustavo E.. "Analytic energy gradient for the projected Hartree–Fock method." <i>The Journal of Chemical Physics,</i> 140, no. 20 (2014) AIP Publishing: http://dx.doi.org/10.1063/1.4876490.https://hdl.handle.net/1911/94380We 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.engArticle is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.Journal articlehttp://dx.doi.org/10.1063/1.4876490