Influence of the intermolecular electrostatic potential on properties of polar polarizable aprotic solvents

Long-Range Orientational Organization of Dipolar and Steric Liquids

Long-range orientational correlations in liquids have received recent renewed interest, in particular for the neat water case. These long-range orientational correlations, exceeding several tens of nanometers, originate from the presence of the strong permanent water dipolar moment. However, the exact dependence with the dipolar moment and the role of other local forces like steric hindrance has never been addressed. In this work, we experimentally measure long-range correlations for a set of liquids differing by their molecular weight and dipolar moment, in order to reveal the origin of their long-range organization. Hence, we show that the dipolar moment of a solvent molecule is not the unique feature determining the orientational correlation. Steric hindrance significantly helps to structure the liquids as well. In order to quantify these long-range correlations, we also derive theoretically the polarization resolved second harmonic scattering intensity as a function of the rotational invariants describing the dipolar and octupolar interaction.

Calculation of the Microscopic and Macroscopic Linear and Nonlinear Optical Properties of Liquid Acetonitrile. II. Local Fields and Linear and Nonlinear Susceptibilities in Quadrupolar Approximation

A discrete model based on the multipolar expansion including terms up to hexadecapoles was employed to describe the electrostatic interactions in liquid acetonitrile. Liquid structures obtained form molecular dynamics simulations with different classical, nonpolarizable potentials were used to analyze the electrostatic interactions. The computed average local field was employed for the determination of the environmental effects on the linear and nonlinear electrical molecular properties. Dipole-dipole interactions yield the dominant contribution to the local field, whereas higher multipolar contributions are small but not negligible. Using the effective in-phase properties, macroscopic linear and nonlinear susceptibilities of the liquid were computed. Depending on the partial charges describing the Coulomb interactions of the force field employed, either the linear properties (refractive index and dielectric constant) were reproduced in good agreement with experiment or the nonlinear properties [third-harmonic generation (THG) and electric field induced second-harmonic (EFISH) generation] and the bulk density but never both sets of properties together. It is concluded that the partial charges of the force fields investigated are not suitable for reliable dielectric properties. New methods are probably necessary for the determination of partial charges, which should take into account the collective and long-range nature of electrostatic interactions more precisely.