Solvation nonelectrostatic contribution

In the previous section, various methods employed to calculate the electrostatic contributions to the free energy of solvation have been presented. However, it is important to provide some ideas about the calculation of nonelectrostatic contributions. These factors are essential for solutes, which are neither charged nor polar. The cavity and van der Waals terms can be combined and represented as [5]... 

The difference of the standard free enthalpies of two different solvates of a certain metal ion may be considered as due to the superimposition of electrostatic and nonelectrostatic contribution 124X... 

The broad applicability often claimed lor Eq. (j) of 12.3.7.2, therefore, needs to be tempered with an awareness of its often serious limitations . Large breakdown in the applicability of such simple relationships may result from several factors, such as nonelectrostatic contributions to the work terms, differences in between corresponding homogeneous and heterogeneous reactions, and specific solvation effects. Further measurements of electrochemical-rate parameters with due regard for double-layer effects are needed to resolve this question. 

The nonelectrostatic contribution to the solvation energy consists of two parts the energy of creating a cavity in solvent and the energy of nonpolar interactions, or van der Waals energy, Uv dw- From theoretical considerations, the free energy of creating a cavity in a solvent should depend on the surface area (S) and on the volume (V) of a solute [68] ... 

The various continuum solvation models may differ in many respects and several classifications have been proposed (Tomasi and Persico [69], Cramer and Truhlar [79]). They may differ on (a) how the size and shape of the cavity is defined (b) how the nonelectrostatic contributions are eomputed (c) how the reaction field is determined (d) how the solute M is described, classically or quantum mechanically. 

Mozgawa K, Mennucci B, Frediani L. Solvation at surfaces and interfaces a quantum-mechanical/continuum approach including nonelectrostatic contributions. J Phys Chem C. 2014 118(9) 4715-4725. http //dx.doi.org/10.1021/jp4117276. 

Electrostatics is certainly the most important interaction between a dielectric medium and a molecular species. Therefore, it has also been investigated extensively for interfaces as shown in the previous section. Nonelectrostatic forces are often neglected in the bulk solution since their contribution to the solvation energy is often limited because of reciprocal cancellation and their effect on molecular properties is small [16] (repulsion and particularly dispersion) or zero (the present understanding of cavitation is strictly empirical). 

The Henry s law constants (77) for triazine-derived herbicides have been calculated using quantum-chemical solvation models, SM2, SMS, PCM-DFT, and CPCM-DFT, and their performances have been discussed. The results showed considerable differences in performance among the different levels of theory. The differences were discussed in terms of the different contributions, electrostatic and nonelectrostatic, to Gibbs free energy of solvation <2003JCI1226>. 

Ion solvation is the transfer of ions from a vacuum to an infinitely dilute solution in a solvent S. In order for us to represent solvation by models, the ion-solvent interactions are split into electrostatic, nonelectrostatic, and chemical contributions. 

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