Complete active space spin-flip methods (SF-CAS) offer an almost black-box single-reference framework for describing the electronic structure of ground and excited states of molecules that may exhibit strong electron correlations, such as metal complexes with multiple metal sites.  The challenge is to formulate and implement methods within this framework that are feasible enough to apply to relatively large molecules (for instance over 50 atoms), and accurate enough to be useful.  This talk will describe some recent progress towards this goal, utilizing non-orthogonal orbitals to relax ionic configurations, as well as excitations that are external to the active space to describe dynamic correlation effects.  These new spin flip methods can be synergistically combined with new ideas that permit treatment of an important class of transition metal systems that contain many strongly correlated electrons within minimally entangled wavefunctions.  The resulting ability to treat large systems with large numbers of strongly correlated electrons will be illustrated with a number of examples.

New developments in complete active space spin-flip methods for ground and excited states of large molecules with strong electron correlations

249th National Meeting (2015)

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