Polarization effects on the structure and dynamics of ionic liquids are investigated using molecular dynamics simulations. Four different ionic liquids were simulated, formed by the anions Cl(-) and PF6(-), treated as single fixed charge sites, and the 1-n-alkyl-3-methylimidazolium cations (1-ethyl and 1-butyl-), which are polarizable. The partial charge fluctuation of the cations is provided by the electronegativity equalization model (EEM) and a complete parameter set for the cations electronegativity (χ) and hardness (J) is presented. Results obtained from a non-polarizable model for the cations are also reported for comparison. Relative to the fixed charged model, the equilibrium structure of the first solvation shell around the imidazolium cations shows that inclusion of EEM polarization forces brings cations closer to each other and that anions are preferentially distributed above and below the plane of the imidazolium ring. The polarizable model yields faster translational and reorientational dynamics than the fixed charges model in the rotational-diffusion regime. In this sense, the polarizable model dynamics is in better agreement with the experimental data.

Raman band-shape analysis of croconate dianion, C 5 O 5 2− , was performed in order to reveal the short-time dynamics of this species in different environments: aqueous solution, acetonitrile solution, and the lowtemperature molten salt tetra(n-butyl)ammonium croconate, [(n-C 4 H 9 ) 4 N] 2 C 5 O 5 ·4H 2 O, TBCR. Two totally symmetric normal modes were investigated, the C-O stretching, n 1 , and the ring breathing, n 2 . Vibrational dephasing parameters for n 1 and n 2 display very different behaviour on changing the environment in which the C 5 O 5 2− moiety is located. A quantitative explanation of the changes in parameters is not yet available, but it is argued that strong hydrogen bond with water molecules is the origin of the very different dephasing dynamics of C 5 O 5 2− in aqueous solution in comparison with acetonitrile solution and TBCR. Thus, experimental vibrational time correlation functions nicely illustrate distinct sensitivity of different intramolecular oscillators of the solute to intermolecular dynamics, that is, distinct coupling between intra-and intermolecular degrees of freedom.

Molecular dynamics simulations are used to investigate structural and dynamical properties of liquid mixtures of water and ethanol over the entire range of compositions from neat liquid water to neat liquid ethanol. Particular emphasis is given to the time relaxation of the anisotropic collective polarizability and the low-frequency part of the depolarized Raman spectra. While the dynamics was carried out using simulations with standard force fields for water and ethanol, the post-analysis was performed employing the chemical potential equalization (CPE) method. For comparison purposes, the CPE results are compared to those obtained with the traditional interaction-induced model. Both methods are able to capture the basic shape and position of the Raman bands. Polarizability response in time and frequency domains is disentangled in permanent, interaction-induced and induced-permanent (cross) terms. Our findings suggest that the polarizability relaxation of water is more sensitive to environmental fluctuations. Once water signal remains covered by the ethanol contribution even in waterrich concentrations, some water polarizability features were unveiled and correlated with H-bond dynamics. The permanent term, representative of the reorientational dynamics, captures the short-time oscillations and responds for a part of the total relaxation, while the long-range interaction-induced contribution is responsible for great part of the total polarizability relaxation.

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