DOUBLE MANY-BODY EXPANSION POTENTIAL-ENERGY SURFACE FOR GROUND-STATE HCN BASED ON REALISTIC LONG-RANGE FORCES AND ACCURATE AB-INITIO CALCULATIONS

A single-valued double many-body expansion potential energy surface is reported for ground-state HCN based on a realistic representation of the long-range forces, and a fit to accurate ab initio calculations fo r the HCN <----> CNH regions [J. M. Bowman, B. Gazdy, J. A. Bentley, T . J. Lee, and C. E. Dateo, J. Chem. Phys. 99, 308 (1993)] and novel fu ll valence complete active space energies for CHN geometries. The vari ous topographical features of the novel global potential energy surfac e are examined, and vibrational calculations are presented to characte rize the minima associated to the HCN and CNH isomers. The quality of the new fit is compared with that of the seminumerical representation of Bowman et al. in terms of root-mean-squared deviations for stratifi ed energy regimes. (C) 1997 American Institute of Physics.