AN AB-INITIO STUDY OF THE FCP POTENTIAL-ENERGY SURFACE

The potential energy surface of FCP was studied with high-level single-reference electron correlated optimization. It was found that linear FPC is a potential energy minimum at the RMP2 and RMP4 levels of theory but a maximum at UMP2, RPM3, UMP3 and UMP4. Moreover, various numbers of minima (Min) and saddle points (TSs) were found on the restricted and unrestricted MPn (n = 2-4) surfaces: 3 Min and 2 TSs on RMP2, 3 Min and 3 TSs on UMP2, 2 Min and 2 TSs on RMP3, 3 Min and 3 TSs on UMP3, 3 Min and 2 TSs on RMP4, and 3 Min and 3 TSs on UMP4. However, at the more reliable quadratic CI and Brueckner doubles levels of theory, only two minima, corresponding to linear FCP and bent FPC (bond angle about 110 degrees), and two saddle points were found on the potential energy surface.