Energy switching approach to potential surfaces. II. Two-valued function for the water molecule

A recently proposed energy switching scheme is used to improve the two-valued many-body expansion potential energy surface of Murrell, Carter, Mills, and Guest [Mol. Phys. 42, 605 (1981)] for H2O by merging it with the spectroscopically accurate polynomial-type form of Polyanski, Jensen, and Tennyson [J. Chem. Phys. 105, 6490 (1996)]. An attempt is also made to improve its long range forces, and Coulombic behavior at the collapsed molecular limits. The resulting ES two-valued surface has almost spectroscopic accuracy up to 13 650 cm−1, and like the original many-body expansion form may be used for studies of reaction dynamics. A brief analysis of the Σ–Π locus of conical intersection is also presented.