Influences on the calculation of accurate and basis set extrapolated oscillator strengths: the transition of H2O

The vertical optical oscillator strength (OOS) for the transition was calculated using complete active space self-consistent field followed by multireference configuration interaction (CAS/MR-CI) wavefunctions and Gaussian basis sets of the aug-cc-pVXZ and d-aug-cc-pVXZ types ( X = D , T , Q , 5). We discuss the dependence of the results on the size of the CAS space, the MR-CI calculation and the Gaussian basis set. The results were extrapolated using the F ( X ) = A + B exp(− CX ) function. The oscillator strengths were obtained at the length ( f L ) and velocity ( f V ) forms. The most extensive treatment gave f L and f V values, with extrapolated values between brackets, 0.048 74 (0.048 71) and 0.054 15 (0.054 12), respectively.