Revised Anisotropic Site Potentials for the Water Dimer and Calculated Properties

Abstract

Two new parametrizations of a recent ab initio polarizable anisotropic site potential for water are presented. The new versions improve the description of the electrostatic interactions, add an explicit charge-transfer term, and use more accurate dispersion coefficients from the recent literature. To assess the merits of the new models, the potential energy surface of the dimer is analyzed and a comparison is made with 12 other polarizable potentials for water in the literature, most of them being currently used in computer simulation. The structure, energy, and harmonic intermolecular frequencies of the stationary points have been determined and compared with the best available ab initio calculations. The energy barriers and pathways for hydrogen atom interchange within the dimer are discussed. The second virial coefficient B ( T ) of steam between 373 and 973 K, including first-order quantum corrections, is reported. For all the models, the quantum corrections are found to be significant at the lowest temperatures, amounting to 10−15% at 373 K. Roughly 90% of the quantum corrections arise from the rotational degrees of freedom. Among the potentials considered, only those presented in the present work and a few others are really successful in reproducing the experimental results for B ( T ) in that temperature range.