Multiconfiguration pair-density functional theory (MC-PDFT) has been shown to yield accurate electronic energies for strongly correlated molecular systems and to predict reliable electronic excitation energies, barrier heights, and bond energies. However, the nonvariational character of MC-PDFT with respect to the wave function parameters impedes direct evaluation of molecular properties that depend on electron density. Here, we derive and implement an analytic expression for the MC-PDFT electric dipole moment by using the method of Lagrange multipliers. We assess the accuracy of predicted dipole moments at equilibrium and nonequilibrium geometries on a series of organic radicals and first-row transition metal diatomics whose wave functions exhibit significant contributions from multiple Slater determinants. We show that MC-PDFT and its hybrid extension (HMC-PDFT) with respectively the tPBE and hybrid tPBE0 on-top density functionals perform as well or better than second-order multireference perturbation theory (CASPT2) and multireference configuration interaction with single and double excitations and a quadruples correction (MRCISD+Q) at greatly reduced computational cost. The mean unsigned deviations from experimental dipole moments of CASSCF, MC-PDFT, and HMC-PDFT are respectively 0.77, 0.29, and 0.24 D.

Dipole moments of strongly correlated molecules: Assessment of multiconfiguration pair-density functional theory and hybrid multiconfiguration pair-density functional theory

ACS Spring 2022

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