Solvation energy calculation

The solvation energies calculated with the Huron-Claverie model were added to the MINDO/3 heats of formation for all species according to Eq. (7). 

In the Coulomb term, the electrostatic and solvation effects depending on the polarity of the media are summarized. For solvent-separated ion pairs (solvation energy calculated by the Born equation), it is given by... 

Various thermodynamic cycles are used in pKa calculations. Although previously a source of confusion in the field, it is now clear that as long as the most accurate experimental values are used, and no explicit water molecules are added, the choice of cycle should just be a matter of convenience. The most common is based on Eq. (1) and is diagramed in Figure 1, where a molecule is simply deproto-nated, yielding a corresponding base and the proton in solution [1,2,4]. This cycle depends on the accuracy of the continuum model used to determine the anion (reaction 1) or cation (reaction 8) solvation energies, calculations that vary in... 

We have recently started to explore a type of calculations in which DFT treatment of the quantum mechanical (QM) site is combined with either continuum electrostatics treatment of the protein, or with microscopic molecular mechanics/dynamics treatment of the protein, or with a combined molecular mechanics and continuum electrostatics treatment of the protein in a truly multiscale type of calculations. All these calculations have a spirit of QM/MM (quantum mechanics combined with molecular mechanics) method, which is currently in wide use in protein calculations. The DFT and the solvation energy calculations are performed in a self-consistent way. The work aims at both improving the QM part of p/ calculations and the MM or electrostatic part, in which of the protein dielectric properties are involved. In these studies, an efficient procedure has been developed for incorporating inhomogeneous dielectric models of the proteins into self-consistent DFT calculations, in which the polarization field of the protein is efficiently represented in the region of the QM system by using spherical harmonics and singular value decomposition techniques [41,42]. 

Among the several available models, those that represent the solvent molecules through a continuum medium are by far the most extensively used in and solvation energy calculations. Thus, we will concentrate the discussion on the continuum approaches but since this is not the main objective of this chapter only the basic ideas will be presented. For more comprehensive discussions, the reader is referred to the excellent reviews of Tomasi and Persico [69], Cramer and Thrular [76], and Orozco and Luque [77]. 

Table 12.1 Solvation energies calculated with the differential geometry nonpolar solvation model for a set of 11 alkanes in comparison with an explicit solvent model [154]...

Figure 4 Schematic of a solvation energy calculation. The initial state treats the solute in a homogeneous dielectric material with both solvent and solute dielectric coefficients set to solute value Ep. The final state involves an inhomogeneous dielectric coefficient with solute value Ep and bulk solvent value Ej.

Figure 12.2.7. General scheme of the theoretical approach for the solvation energy calculation.

Craw et al. used the PCM as well as Monte Carlo approaches in their study of this problem. The gas phase barrier heights obtained by CCSD(T)/cc-pVTZ calculations are 15.5 and 16.9 kcal mol. Adding on the PCM solvation energies, calculated at the SCF level with the cavity defined by a 0.001 e isodensity surface, results in barrier heights of 19.0 and... 

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