A multireference version of generalized Epstein-Nesbet type perturbation theory is presented. For the single reference case, as shown by Surjan and Szabados, the third-order energies are identically zero and low order corrections (2nd,4th) are quite accurate. The formalism holds also for multireference case, and the results are expected to be even more accurate.

A multireference version of generalized Epstein-Nesbet type perturbation theory is presented. For the single reference case, as shown by Surjan and Szabados, the third-order energies are identically zero and low order corrections (2nd,4th) are quite accurate. The formalism holds also for multireference case, and the results are expected to be even more accurate.