THE STRUCTURE AND STABILITY OF THE O2(2+) DICATION - A DRAMATIC FAILURE OF MOLLER-PLESSET PERTURBATION-THEORY

By comparison with results of full configuration-interaction and large-scale multireference configuration-interaction calculations, it is shown that the widely used RMP2 and RMP4 methods fail to describe even qualitatively the structure and kinetic stability of the O2(2+) dication, an isoelectronic analogue of molecular nitrogen. A barrier to dissociation of more than 200 kJ mol-1 completely disappears. In contrast, much better results are obtained from other methods based on a single reference function, such as quadratic configuration interaction and the Brueckner doubles procedure.