A polarizable embedding approach to second harmonic generation (SHG) of molecular systems in aqueous solutions

We present the extension to second harmonic generation (SHG) of the atomistic fully polarizable QM/FQ method that treats the solvent atomistically and embeds each atom in the solvent with a fluctuating charge (FQ) which responds to the solute quantum mechanical (QM) electrostatic potential in a self-consistent manner. The proposed approach is able to achieve an adequate modeling of solvent effects both in the quantum mechanical response equations and on the conformational properties of the system, which is sampled by resorting to molecular dynamics simulations. The application of the model to selected organic acids in aqueous solution, for which the interaction with the surrounding environment is dominated by HB interactions, shows a good agreement in both the modeling of solvent effects and in the reproduction of experimental SHG data extracted from hyper-Raman scattering experiments.