Potential, intermolecular Terms Links

Fugacity and activity are basically compositional terms. In ideal solutions they are not necessary pressure and various composition terms can be directly linked to the Gibbs energy. Real solutions have a variety of intermolecular forces, so that ideal solution models need correction factors. These corrections can be made either to the composition terms (fugacity and activity coefficients) or to the thermodynamic potentials (excess functions), and efforts to model these correction factors in mathematical terms have always been, and likely always will be, an important research field. 

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). 

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