H2O photodissociation dynamics based on potential energy surfaces from density functional calculations

Abstract

We investigate the usefulness of density functional theory (DFT) for calculating excited state potential energy surfaces. In the DFT calculations, the generalized gradient approximation (GGA) is used. As a test case, the photodissociation of H2O through the first excited à 1B1 state was considered. Two-dimensional potential energy surfaces were obtained for both the X̃ 1A1 ground state and the first excited state. Wave packet calculations employing these surfaces were used to obtain both the absorption spectrum and partial photodissociation cross sections, which are resolved with respect to the final vibrational state of the OH fragment. Comparisons are made with a previously calculated high level ab initio potential energy surface, with dynamics calculations using that surface, and with experiment. The vertical excitation energy for the (X̃ 1A1→à 1B1) transition calculated using DFT is in good agreement with the previous ab initio calculations. The absorption spectrum and the partial cross sections obtained with the DFT treatment are in good agreement with experiment.