The spin-flip ("SF") method allows for description of multi-configurational states by considering excitations of a single high-spin reference state. It was originally developed for use with wavefunction-based approaches such as equation-of-motion coupled-cluster ("EOMSF-CC" or "SF-CC") and configuration interaction ("SF-CI"), and later extended for use with the density-functional-based linear-response approach of time-dependent density-functional theory (SF-TDDFT). SF-TDDFT, SF-CI, and SF-CC approaches have been used to describe the energies of various electronic states of open- and closed-shell atoms and molecules due to its ability to adequately describe electronic ground- and first-excited-state conical intersections. The GW/Bethe-Salpeter approach ("GW/BSE") is akin to TDDFT but with an ab initio long-ranged and non-local interaction kernel, which allows for an improvement in caclulation of excited-state energies. We consider a spin-flip GW/BSE ("SF-BSE") approach to improve SF-TDDFT. This method has a more moderate expense than FCI, SF-CISD or SF-CCSD, and SF-BSE can be used also for extended systems. We present the theory of SF-BSE and apply it to simple molecular examples such as the ethylene torsion potential and CuO, Cu<sub>2</sub>O, and CuO<sub>2</sub> anions.

Spin-flip Bethe–Salpeter equation approach and applications to simple molecular systems

2019 Fall National Meeting

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