Anab initiostudy of the non-linear optical properties of the He atom and the H2molecule

Using the steady state formulation of the time-dependent Schrödinger equation a systematic examination has been undertaken of the frequency dependent dipole polarizabilities and third order susceptibilities for the helium atom and the hydrogen molecule. Full configuration interaction wavefunctions determined using large basis sets were employed. For both systems the calculated dipole polarizabilities are in excellent agreement with the best known results. For the calculated non-linear susceptibilities-the frequency dependent hyperpolarizability and the coefficient of the third harmonic generation-the results are estimated to be accurate to within a few per cent.