The polynomial cost in complete active space self-consistent field (CASSCF) computations can be realized through variational optimization of the active-space two-electron reduced-density matrix (2-RDM). Although, similar to conventional approaches to CASSCF, variational 2-RDM (v2RDM)-driven CASSCF captures nondynamical electron correlation in the active space, it lacks a description of the remaining dynamical correlation effects. Such effects can be modeled through a combination of v2RDM-CASSCF and on-top pair-density functional theory (PDFT). The resulting v2RDM-CASSCF-PDFT approach provides a computationally inexpensive framework for describing both static and dynamical correlation effects in multiconfigurational and strongly correlated systems. Our generalized version of MCPDFT incorporates the hybrid, double-hybrid and range- separated on-top pair-density functionals. These functionals can be derived from familiar Kohn-Sham exchange-correlation density functionals through the translation of the v2RDM-CASSCF reference densities. The resulting translated and fully-translated on-top PDFT functionals are then applied to the variety of strongly correlated systems including single- and double-dissociation potential energy curves of N2, H2O, respectively, as well as to the singlet/triplet energy splittings in the linear polyacene series.

Multiconfigurational pair-density functional theory: Strong-correlation method in quantum chemist's toolbox

2019 Fall National Meeting

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