Towards quantitative diatomics-in-molecules model for the water molecule

The diatomics-in-molecules (DIM) model is developed for the water molecule which allows us to extend the set of molecular parameters quantitatively predicted with the help of this theory. It is shown that not only mixing of the neutral and ionic states when constructing the polyatomic basis functions as prescribed by the previous works is necessary for an accurate description of the ground state potential energy surface, but certain corrections due to a multicenter charge distribution in the polyatomic molecule are required. The results of new ab initio calculations for the potential curves of the ion-pair states of OH are employed. Finally, the energies of H2O are obtained from the 9 X 9 DIM Hamiltonian matrix what makes feasible further applications of this surface in molecular dynamics simulations of water containing intermolecular complexes. The molecular constants predicted by DIM including harmonic frequencies are perfectly consistent with the reference data. The H2O potential energy surface of spectroscopic accuracy created by Partridge and Schwenke have been used for the point-by-point comparison of DIM and ab initio results showing the efficiency of the present model. (C) 1998 Elsevier Science B.V. All rights reserved.