The Water Dimer: Post-Hartree-Fock and Density Functional Calculations on the Potential Energy Surface

Abstract

Conventional ab initio and density functional methods with extended basis sets were employed in the study of a path on the water-dimer potential energy surface. The results show that density functional methods do depend strongly on the type of exchange-correlation potential employed, as well as on the quality of the basis sets – similarly to conventional ab initio methods – and on the density of the grid. Gradient-corrected methods behave, as expected, better than uncorrected ones, the Becke–Lee–Yang–Parr (BLYP) potential being the one that gives the best results. However, too large chemical- and hydrogen-bond lengths and absolute energies, as well as too small relative total and correlation energies demonstrate that even BLYP calculations with a relative large basis set are not good as MP2 calculations of the same size. Adiabatically connected functionals (ACM), represented in this work by B3PW91, provide an improvement on the whole surface.