Optimized semiempirical potential energy surface for H2 16O up to 26000 cm-1

A semiempirical potential energy surface is obtained for the major isotopologue of the water molecule H-2 O-16 that allows the vibration-rotation energy levels in the range of 0-26000 cm(-1) to be calculated with an accuracy almost equal to the average experimental accuracy of measurements in the infrared and visible ranges. Variational calculations using this potential energy surface reproduce the experimental energy values of more than 1500 vibration-rotation levels of H-2 O-16 with the total angular momentum quantum number J = 0, 2, and 5 in the indicated range with a standard deviation of 0.022 cm(-1). The potential was obtained by optimizing a starting ab initio surface using a combination of two approaches, i.e., (1) the multiplication of the starting ab initio surface by a morphing function whose parameters were optimized and (2) the optimization of parameters of the ab initio surface using both the experimental values of energy levels and the results of quantum-chemical electronic structure calculations.