C. Angeli et al., On a mixed Moller-Plesset Epstein-Nesbet partition of the Hamiltonian to be used in multireference perturbation configuration interaction, CHEM P LETT, 317(3-5), 2000, pp. 472-480
Within the frame of second-order multi-reference perturbation theory (MR-PT
), drawing on previous work of Dyall, a new partition of the Hamiltonian, w
hich can loosely be considered as intermediate between Moller-Plesset (MP)
and Epstein-Nesbet (EN), is presented. The method, which is well suited for
CAS-SCF zero-order wavefunctions, is expected to correct partially the def
ects of MP and EN while retaining their good properties. The new approach h
as been successfully applied to some test cases involving the homonuclear d
iatomics F-2, Cl-2 and N-2 where the faults of the EN treatment appear to b
e in large measure eliminated. Application to the Cr, diatomic shows that t
he dramatic intruder state problem suffered by the MP treatment is complete
ly solved, affording a qualitatively good description of the potential ener
gy curve for the ground state. (C) 2000 Elsevier Science B.V. All rights re
served.