Polarizable interaction potential for water from coupled cluster calculations. I. Analysis of dimer potential energy surface

Abstract

A six-dimensional interaction potential for the water dimer has been fitted to ab initio interaction energies computed at 2510 dimer configurations. These energies were obtained by combining the supermolecular second-order energies extrapolated to the complete basis set limit from up to quadruple-zeta quality basis sets with the contribution from the coupled-cluster method including single, double, and noniterative triple excitations computed in a triple-zeta quality basis set. All basis sets were augmented by diffuse functions and supplemented by midbond functions. The energies have been fitted using an analytic form with the induction component represented by a polarizable term, making the potential directly transferable to clusters and the bulk phase. Geometries and energies of stationary points on the potential surface agree well with the results of high-level ab initio geometry optimizations.

New ab initio potential energy surface and the vibration-rotation-tunneling levels of (H2O)2 and (D2O)2

“…Calculations on the effects of monomer flexibility [18][19][20] have shown that this quantity a͑0͒ + a͑1͒ decreases when the H 2 O monomers are relaxed. It is striking in this respect, see Table VI, that the other pure ab initio potential that gives very good agreement with the experimental data, the 6D CC-pol potential, 10,17,21 gives practically the same deviation from experiment for a͑0͒ + a͑1͒ as the HBB0 and HBB potentials. It is most probable that all of these potentials have reached the "rigid monomer limit" of the acceptor splitting.…”

Water trimer torsional spectrum from accurate ab initio and semiempirical potentials

“…The value of D e from the HBB+ 3B potential is too small, which is due to the fact that the HBB pair potential is too shallow. 28 In Tables II and III, we see that the torsional frequencies of both ͑H 2 O͒ 3 and ͑D 2 O͒ 3 do not change much by the inclusion of the three-body induction terms: the splittings decrease for ͑H 2 O͒ 3 by 2%-3%. The frequencies are increased by 2%-3% compared to the CC-pol͑2B͒ values when the complete three-body potential is used, including exchange.…”

“…31 turned out to reproduce the spectra of ͑H 2 O͒ 2 and ͑D 2 O͒ 2 very precisely, even more so than the best of the VRT͑ASP-W͒ potentials 42 fitted to the latter spectrum. Several of these potentials [26][27][28][29]42,44 have also been used in molecular dynamics ͑MD͒ simulations of liquid water. An extensive discussion of their performance in this respect can be found in Ref.…”

“…Reference 25 reviews the work up to the year 2000. Several ab initio water pair potentials have been obtained recently, with [26][27][28][29] or without 30,31 explicit inclusion of the polarization effects that form the dominant contribution to the many-body interactions in water. These water pair potentials were tested by a computation 29,31 of the vibration-rotation-tunneling ͑VRT͒ levels of the water dimer and comparison with the available high-resolution terahertz spectra.…”

“…[26][27][28]42 With the CC-pol potential of Refs. 27 and 28 three-body exchange interactions are available as well, 45 and we included these in the calculation of the water trimer levels.…”