Real-space pseudopotential calculations of the ground-state and excited-state properties of the water molecule

Abstract

Excitation energies, normal modes of vibration and geometries of the electronically excited states of the water molecule are calculated using time-dependent density functional theory with ab initio pseudopotentials and the local density approximation. We express electronic orbitals on a real-space grid with no explicit basis set; as such, no polarization functions are required. Convergence is controlled by a single parameter, the grid spacing. It is found that for the first and second excited states the time-dependent local density approximation predicts a metastable configuration, in disagreement with published results using asymptotically corrected functionals that correctly predict the photodissociation of the molecule. It is shown that applying the real space method with the asymptotically corrected local density approximation reproduces the previous results. The polarizability of the water molecule is calculated using the time dependent local density approximation as well as using the asymptotically corrected local density approximation.