Configuration interaction and relaxation effects on generalized and optical oscillator strengths of the H2O molecule: The X1A1 → A1B1 transition

Generalized and optical oscillator strengths for the X1A1 → A1B1 transition in H2O were computed. Several wavefunctions with variable correlation levels, ranging from complete active space self consistent field to multireference configuration interaction, were employed. Three different Gaussian basis sets were used. Orthogonal and non-orthogonal molecular orbitals, the latter providing direct inclusion of relaxation effects in the excited states, were considered. The effect of these three degrees of approximations, namely, wavefunction quality, basis set type and molecular orbitals, on the accuracy of the generalized and optical oscillator strengths, were systematically investigated. Comparison with previous theoretical and experimental results was performed.