We propose a method for calculating second-order induction and dispersion energies for weakly interacting multireference systems in arbitrary electronic states. It is based on response properties obtained from extended random phase approximation (ERPA) equations. The introduced formalism is general and requires only one- and two-particle reduced density matrices of monomers. We combine the new method with either generalized valence bond perfect pairing (GVB) or complete active space self consistent field (CASSCF) description of the interacting systems. We also explore a hybrid approach combining DFT and multireference wavefunction methods via range-separation. In addition to a general scheme, three approximations to the dispersion energy exploiting Dyall partitioning of the monomer Hamiltonians are introduced, leading to significant reduction of the computational cost.

Second-order dispersion and induction energies based on multireference description of monomers

2019 Spring National Meeting

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