Spin-flip configuration interaction singles with exact spin-projection: Theory and applications to strongly correlated systems.

摘要: Spin-flip approaches capture static correlation with the same computational scaling as ordinary single reference methods. Here, we extend spin-flip configuration interaction singles (SFCIS) by projecting out intrinsic spin-contamination to make it spin-complete, rather than explicitly complementing spin-coupled configurations. We give a general formalism of spin-projection for SFCIS, applicable any spin states. The proposed method is viewed natural unification SFCIS and spin-projected CIS achieve better qualitative accuracy at low cost. While our wave function ansatz more compact previously spin-complete SF approaches, successfully offers beyond biradicals without sacrificing good quantum numbers. It also shown that invariant respect open-shell orbital rotations, due uniqueness spin-projection. will report benchmark calculations demonstrate its performance on strongly correlated systems, including conical intersections appear both in ground-excited excited-excited degeneracies.