Molecular model potential well profile

While the detailed analysis of the Kerr profiles in pure liquids leads to the conclusion that four distinct responses underlie the overall rise and decay of the field-induced polarization anisotropy A n(t), naturally in a real liquid these responses are coupled together. For clarity of discussion we will continue to describe them separately, since the timescale separation assumption in Eq. (3) proved quite valid. Summarized as follows in terms of r (t), which are associated with the instantaneous electronic and noninstantaneous, field-driven nuclear responses linked to intra- and intermolecular motions, the responses are labeled r (electronic) and r2> r, r (nuclear). The underlying assumption of a harmonic potential v j, and a continuum fluid [g(r) = 1] might clearly lead to some over simplifications but if molecules reside at or near the bottom of the potential well, the situation is not unreasonable. The results are very instructive for modeling short-time behavior for molecular solvents at room temperature, which is the next, vastly more complex step (see references on simulations and the next chapter). 

Another model which combined a model for the solvent with a jellium-type model for the metal electrons was given by Badiali et a/.83 The metal electrons were supposed to be in the potential of a jellium background, plus a repulsive pseudopotential averaged over the jellium profile. The solvent was modeled as a collection of equal-sized hard spheres, charged and dipolar. In this model, the distance of closest approach of ions and molecules to the metal surface at z = 0 is fixed in terms of the molecular and ionic radii. The effect of the metal on the solution is thus that of an infinitely smooth, infinitely high barrier, as well as charged surface. The solution species are also under the influence of the electronic tail of the metal, represented by an exponential profile. 

Tournassat et al. (2009) compared the BSM and TLM models with molecular dynamics simulations of a montmorillonite/water interface at the pore scale in 0.1 M NaCl. Simulation-derived values were compared with macroscopic model results obtained from the classical models. Although the Na concentration profile is well reproduced in the diffuse layer, anion exclusion is overestimated by the BSM and TLM theories under the experimental conditions employed the agreement between molecular dynamics simulated and modeled diffuse-layer composition is less accurate with TLM than with BSM. However, the potentials at the three planes of interest are accurately reproduced. It was also showed that molecular dynamics simulations can be used to constrain BSM parameters or, in combination with zeta potential measurements, TLM parameters, by providing suitable values for the capacitance parameters. 

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