Correction vector method for exact dynamic NLO coefficients in restricted configuration space

The correction vector technique for obtaining dynamic nonlinear optical (NLO) coefficients is extended to semi-empirical CI schemes. The technique is established by comparison with full sums over states (SOS) computations on a small system. Comparison of the results of a truncated SOS method and the full-space NLO coefficients from the correction vector method in a CI space of 1347 configurations shows that the SOS technique with 50 excited states for para-nitroaniline gives reliable α and β values, but the γ value is off by more than a factor of 2 for the dominant components. The correction vector technique, besides being exact in the chosen CI space, is also computationally more efficient than the truncated SOS technique.