Semiempirical calculations of first-order hyperpolarizabilities: Testing the performance of different methods in comparison to experiment

The performances of three semiempirical program packages for the calculation of frequency-dependent first-order hyperpolarizabilities are tested using a data set of 200 different organic compounds. The methods used are the sum-over-states approaches implemented in VAMP6.0 and CNDOS, and the time-dependent Hartree-Fock (TDHF) method included in MOPAC. For the configuration interaction (CI) calculations in the gasphase single and pair-double excitation (VAMP-PECI) and single excitation CI (CNDOS-SCI) with two different sizes of the active orbital window are used. In the case of MOPAC and VAMP6.0 the AM1 and PM3 Hamiltonians are used. Although the correlation coefficients, r, obtained are slightly different, all calculational methods are comparably useful for trend predictions in the molecular design of new compounds for nonlinear optical applications. Because of the enormous computational costs, the TDHF method is only feasible for smaller molecules or smaller data sets. To account for solvent effects, the state energies obtained first from gas-phase CI calculations are corrected using the self-consistent-reaction-field (SCRF) approach implemented in VAMP6.0, improving the quality of the results.