H2O PHOTODISSOCIATION DYNAMICS BASED ON POTENTIAL-ENERGY SURFACES FROM DENSITY-FUNCTIONAL CALCULATIONS

We investigate the usefulness of density functional theory (DFT) for c alculating excited state potential energy surfaces. In the DFT calcula tions, the generalized gradient approximation (GGA) is used. As a test case, the photodissociation of H2O through the first excited (A) over tilde B-1(1) state was considered. Two-dimensional potential energy s urfaces were obtained for both the (X) over tilde (1)A(1) 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 w ith a previously calculated high level ab initio potential energy surf ace, with dynamics calculations using that surface, and with experimen t. The vertical excitation energy for the ((X) over tilde (1)A(1)--> ( A) over tilde B-1(1)) transition calculated using DFT is in good agree ment 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. (C) 1995 American Institute of Physic s.