A new density functional theory was recently developed: multiconfiguration pair-density functional theory (MC-PDFT)[1]. As opposed to modeling the electronic structure of a system by a single electronic configuration, as is the case of time-dependent Kohn-Sham density functional theory (TD-KS-DFT), MC-PDFT uses multiple electronic configurations that are obtained using a multiconfigurational self-consistent field (MCSCF) method. In MC-PDFT, the energy consists of the MCSCF electronic kinetic energy, the classical Coulombic interactions of electrons and nuclei, and the on-top energy. The on-top energy plays an analogous role to the exchange-correlation energy from KS-DFT but is a functional of the MCSCF density and on-top pair density. This work focuses on extending MC-PDFT to self-consistently optimize the configuration interaction (CI) coefficients of the MCSCF wave function in the presence of the on-top potential. Specifically, we are investigating the diagonalization of an effective MC-PDFT Hamiltonian. The result may not only provide more accurate energetics but should improve the qualitative description of strongly-interacting states (e.g., at a conical intersection) since electronic couplings are explicitly included. This study is of novel interest to quantum chemistry since dynamical correlation is included in the CI optimization via a density functional, which is less costly than including excitations to high-energy configurations as is common for standard multireference methods (e.g., multireference configuration interaction). [1] Li Manni, G.; Carlson, R. K.; Luo, S.; Ma, D.; Olsen, J.; Truhlar, D. G.; Gagliardi, L., Multi-Configuration Pair-Density Functional Theory. J. Chem. Theory Comp. 2014, 10 (9), 3669-3690.

Configuration interaction under the presence of a density functional

251st National Meeting (2016)

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