During the last few years, we have developed and implemented symmetry breaking and restoration techniques as an alternative to traditional multireference methods for accounting static correlation effects originating from near degeneracies in the wave function. Symmetry implies degeneracy, and self-consistent variation after projection techniques are a powerful tool for accounting them via non-orthogonal Slater determinants. In our work, symmetries deliberately broken and restored include number, spin, complex conjugation, point group, lattice translation, and space group. We have recently implemented analytic energy gradients for these projected Hartree-Fock methods that avoid the evaluation of coupled perturbed equations (as HF itself). A sketch of the theory and some applications to geometry optimization and vibrational frequency evaluation will be presented.

Projected Hartree-Fock energy gradients and applications

248th National Meeting (2014)

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