Relativistic multireference Møller–Plesset perturbation theory based on multiconfigurational Dirac–Fock reference functions

Relativistic multireference Møller–Plesset perturbation theory is developed and implemented with analytic basis sets of Gaussian spinors. The theory takes multiconfigurational Dirac–Fock self-consistent field wavefunctions as reference functions. A procedure is described by which to perform multireference second-order Møller–Plesset perturbation theory calculations for a general class of reference functions constructed from one-particle Dirac spinors. Multireference perturbation calculations are reported for the ground and low-lying excited states of oxygen-like iron, Fe18+ (Z=26), and ground-state Zn0, in which the near degeneracy of a manifold of strongly interacting configurations mandates a multireference treatment.