Correlated electronic structure methods provide a rich framework to formulate systematically-improvable theories of ground and electronic excited states. In this talk, I will describe our efforts to develop low-cost and robust correlated methods that can be applied to study near-degenerate ground and excited states. The basis of our approach is the similarity renormalization group (SRG) – a many-body theory to diagonalize operators using a series of infinitesimal transformations. Starting from the SRG, we have recently proposed a driven SRG (DSRG) for Quantum Chemistry applications and used it to derive numerically-robust multireference theories. This talk will focus on perturbative approximations of the DSRG equations and their generalization to treat near-degenerate ground and excited states. In the last part of this talk, I will present benchmark applications of these novel DSRG methods to compute vertical excitation energies and explore avoided crossings and conical intersections.

Electron correlation methods for near-degenerate states based on the driven similarity renormalization group

254th National Meeting (2017)

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