ENERGY SWITCHING APPROACH TO POTENTIAL SURFACES - AN ACCURATE SINGLE-VALUED FUNCTION FOR THE WATER MOLECULE

A novel scheme is suggested to construct a global potential energy sur face by switching between representations which are optimal for differ ent energy regimes. The idea is illustrated for the electronic ground state of water for which we use as switched functions the many-body ex pansion potential of Murrell and Carter [J. Chem. Phys. 88, 4887 (1984 )] and the polynomial form of Polyansky, Jensen, and Tennyson, [J. Che m. Phys. 101, 7651 (1994)]. By also modifying the former to reproduce the Coulombic behavior at the collapsed molecular limits for vanishing ly small interatomic distances and approximately account for the long range forces, the new potential energy surface has been given double m any-body expansion quality. The result is a global H2O potential energ y surface which has spectroscopic accuracy and may be used for studies of reaction dynamics. (C) 1996 American Institute of Physics.