Several ab initio methods are applied to the study of two linear isomers of methylidyne phosphine, HCP, and HPC. Single-reference correlation methods ranging from second-order Møller-Plesset theory to coupled cluster singles and doubles theory with noninterative inclusion of connected triple excitations were applied in a variety of basis sets of increasing size. In addition, complete active space self-consistent field wave functions, multireference singles and doubles configuration interaction, and averaged coupled pair functional theory were also applied to HPC. For HPC comparison of the single-reference based results is made with experimental data and previous theory to assess the accuracy of the methods employed. The same single-reference-bsed methods are then applied to linear HPC in order to assess whether it is a stable minimum or a transition state (imaginary frequencies in two dimensions). It is found that linear HPC is not a minimum on the ground-state potential surface. However, relatively high levels of correlation must be used when single-reference-based methods are employed to arrive at this conclusion. The multireference-based methods are then applied to HPC, and they too predict that it is not a minimum on the ground electronic potential surface. The qualitative nature of linear HPC is examined using CASSCF and CCSD wave functions.
© 1994 American Chemical Society
Hong, H.S. ;Cave, R.J. “A Theoretical Investigation of the Stability of HPC,” J. Phys. Chem. 1994, 98, 10036. DOI: 10.1021/j100091a016