Regular interaction energy

The study of composite cations encounters further problems for classical and conventional QM/MM simulations, as their lower symmetry makes the evaluation of interaction energy surfaces and analytical potential functions describing them difficult. In these cases the QMCF MD method provides an elegant solution as well, renouncing solute-solvent potential functions. This advantage could be well demonstrated in studies on the dimer of Hg(I) (39), the titanyl ion (64), and the uranyl ions of U(V) (65) and U(VI) (66). Whereas the Hg + ion still has a fairly regular hydration structure although with a quite peculiar shape, the... 

Table 70 Angular Overlap Method (AOM) d-Oribital a- and -Interaction Energies for Various Regular Copper(II)...

Fig. 4. The CoMFA process consists of individual steps (adapted from Cramer et al. 1988). First, interaction energies are computed between all molecules in alignment and a probe atom on a regular grid. This information is stored in a particular format in order to allow for multivariate statistical analysis. The PLS method then produces a statistical model which can be interpreted and used for prediction.

Since the Flory interaction parameter, x> was derived by considering only interaction energies between the molecules, it should not contain any entropic contributions and Equation (2D-9) should yield the correct value for the Flory-/ parameter. Unfortunately, x contains not only enthalpic contributions from interaction energies, but also entropic contributions. The solubility parameter includes only interaction energies and by the definition of regular solutions does not include any excess entropy contributions. Blanks and Prausnitz (1964) point out that the Flory / parameter is best calculated from... 

The thermodynamics of non-ideal bulk mixtures has been considered in sec. 1.2.18. Non-idealities can be expressed in terms of activity coefficients, excess functions, pair interaction energies (as In Regular Solution theory) or through vlrlal expansions. For all these methods surface equivalents can be formulated. 

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