Developments in DFT/MRCI for Excited Electronic States

Michael Schuurman\(^{1,2}\) and Simon Neville\(^{1}\)

\(^{1}\) National Research Council Canada
\(^{2}\) Department of Chemistry and Biomolecular Sciences

The combined density functional theory and multireference configuration interaction (DFT/MRCI) method fills a unique niche in the landscape of excited-state electronic structure theory. In particular, DFT/MRCI possesses the folliowing desirable characteristics: (i) the possibility of ''black box" impelementation; (ii) accurate vertical excitation energies; (iii) low computational cost, rendering it applicable to large molecules, and; (iv) an ability to describe a large range of electronic states, including those of multiference, Rydberg, and double-excited, and charge transfer character. Here a number recent developments using this formalism will be described, including a 'pruning' algorithm to remove a priori the deadwood configurations from the CI wave function as well as a perturative approximation the replaces explicit diagonalization of the full DFT/MRCI Hamiltonian with a small, effective Hamiltonian. Both these developments significantly expand:q the range molecules amenable to description using this formalsim.

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