IS HPC A MINIMUM ON THE HCP POTENTIAL SURFACE - A FAILURE OF THE MOLLER-PLESSET PERTURBATION-THEORY

Single reference electron correlated optimizations were carried out fo r linear phosphaethyne (HCP) and isophosphaethyne (HPC) in order to de termine whether HPC is a species capable of existence. It was found th at HPC is a potential energy minimum at the RMP2, RMP4, UMP2, UMP3 and UMP4 levels of theory but a potential energy maximum at RMP3. However , at the more reliable quadratic CI and Brueckner doubles levels of th eory, HPC is found to be a potential energy maximum.