Computer simulation of the linear and nonlinear optical properties of liquid benzene: Its local fields, refractive index, and second nonlinear susceptibility

Molecular dynamics (MD) simulation and subsequent analysis of the macroscop ic polarization developed in response to "a posteriori'' applied electric f ields or of spontaneous fluctuations in the instantaneous polarization unde r zero applied field is used to assess the nonlinear optical properties of a polarizable liquid. Three strategies are proposed for the electrostatic a nalysis, all using as input static "gas phase'' (hyper)polarizabilities, ob tained from ab initio calculations. All three strategies are shown to accur ately reproduce the experimentally measured refractive index and second non linear susceptibility of liquid benzene. The simulation also predicts the d istribution of orientations and magnitudes of the local electric fields exp erienced by the molecules in the liquid, and the nonlinear contributions to the local fields. This approach gives an 8% higher estimate of the second nonlinear susceptibility of liquid benzene than the Lorentz local field fac tor approach, in better agreement with experimental values. (C) 1999 Americ an Institute of Physics. [S0021-9606(99)51612-7].