Is Moller-Plesset perturbation theory a convergent ab initio method?

Recent studies have seriously questioned the use of higher-order Moller-Ple sset perturbation theory (MPn) in describing electron correlation in atomic and molecular systems. Here we first reinvestigate with improved numerical techniques previously controversial and disturbing MPn energetic series fo r Ne, F-, HF, BH, C-2 and N-2. Conspicuously absent in previous work is res earch on the convergence of MPn spectroscopic constants, and thus complete MPn (energy, r(e), omega(e)) series were then computed for (BH, HF, CN+, C- 2 and N-2) through the high orders (MP25, MP21, MP13, MP39 and MP19) within the correlation consistent family of basis sets. A persistent, slowly deca ying ringing pattern in the C-2 energy series was tracked out to MP155. Fin ally, new energy series were generated and analyzed through MP167 for Cl- a nd MP39 for Ar and HCl. The MPn energy and property series variously displa y rapid or slow convergence, monotonic or oscillatory decay, highly erratic or regular behavior, or early or late divergence, all depending on the che mical system or the choice of one-particle basis set. For oscillatory serie s the spectroscopic constants computed from low-order MPn methods are often more accurate, with respect to the full configuration interaction (FCI) li mit, than those computed via high-order MPn theory. (C) 2000 American Insti tute of Physics. [S0021- 9606(00)30221-5].