15min:
ELECTRONIC STATE OF CoH: A PROBLEM RELATED TO THE SIZE-INCONSISTENCY OF THE MR-SDCI METHOD AND THE MIXING OF 3 Phi AND 3 Pi .

REI FUKUI, UMPEI NAGASHIMA AND TSUNEO HIRANO, Grid Technology Research Center, Institute of Advanced Industrial Science and Technology, 6-9-3 Ueno, Taito-ku, Tokyo 110-0015, Japan; HIROSHI TATEWAKI, Computation Center and Institute of Natural Sciences, Nagoya City University, Nagoya 467-8501, Japan; TAKESHI NORO AND KIYOSHI TANAKA, Division of Chemistry, Graduate School of Science, Hokkaido University, Kita 10, Nishi 8, Kita-ku, Sapporo, 060-0810, Japan.

The ground state of CoH has been determined experimentally as the 3 Phi by the far-infrared magnetic resonance study, and theoretically by ab initio methods.\footnoteD.P. Chong, S.R. Langhoff, C.W. Bauschlicher, Jr., S.P. Walch, and H. Partridge, J. Chem. Phys ., 85, 2850-2860 (1986);

M. Freindorf, C. M. Marian, and B. A. Hess, J. Chem. Phys ., \textbf99, 1215-1223 (1993). However, MR-SDCI and MR-SDCI + Q ab initio molecular orbital calculations predicted that the lowest electronic state is 5 Phi .~ The size-consistent MR-ACPF method correctly predicted that 3 Phi should be the ground state.~ As is previously reported by Tanaka et al. on FeH, the controversial results in MR-SDCI may arise through truncation error inherent in the size-inconsistent MR-SDCI method.

Another difficulty is that we cannot clearly separate the Phi and Pi states when CoH is treated under C2v symmetry, not under its real symmetry of Cinfinity v. The best results we obtained at the moment are: re = 1.528 Å, Be = 7.291 cm- 1, and omega e = 2005 cm- 1 at the level of the MR-ACPF + relativistic correction using the Roos ANO (Co) and Dunning aug-cc-pVQZ (H) basis sets.