It is a significant challenge to treat electronic structure problems where strong correlations and low-lying excited states are present, particularly if the molecules are not small.  Spin-flip methods represent a promising approach for treating such problems.  In this talk, the basics of spin-flip methods will first be reviewed, and then the restricted active space spin flip (RAS-SF) method will be discussed in detail.  The RAS-SF method can treat some important classes of strongly correlated problems, and is applicable to large molecules.  A new implementation of the RAS-SF permits unlimited numbers of spins to be flipped, while our previous implementation was limited to two spin flips.  Depending on time and progress, a variety of chemical applications of the new RAS-SF implementation will be described, ranging from biradicaloids (single spin flips) to tetraradicaloids (double spin flips), to spin-coupled transition metal systems (multiple spin flips).

Restricted active space spin flip method for excited states, conical intersections and strong electron correlations

243rd National Meeting (2012)

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