COMPARISON OF RESULTS FROM PARAMETRIZED CONFIGURATION-INTERACTION (PCI-80) AND FROM HYBRID DENSITY-FUNCTIONAL THEORY WITH EXPERIMENTS FOR FIRST-ROW TRANSITION-METAL COMPOUNDS

Different methods and schemes have been tested for the difficult class of first row transition metal complexes. The systems investigated are the M(+), MH(+), MCH(3)(+), and MCH(2)(+) systems for the entire row and the Ni(CO)(x) systems with x = 1-4. In general quite satisfactory results are obtained both at the PCI-80 and hybrid density functional levels. In particular, for the MH(+) and MCH(3)(+) systems the PCI-80 average deviation to experiments is of the same size as the uncertaint y in the experiments. The MCH(2)(+) systems are somewhat more difficul t to describe and a rather large error is found for chromium at the PC I-80 level, due to a large coupling of exchange energy loss and change of correlation energy resulting from the formation of two covalent d- bonds. Scaling at the modified coupled pair functional (MCPF) level is also compared to scaling at the coupled cluster singles and doubles ( CCSD) level. In most cases very similar results are obtained, but clas ses of systems can be identified where scaling works better at the MCP F level and other classes where it works better at the CCSD level. (C) 1996 American Institute of Physics.