Solvation energy definition

On correcting to unit activity Ag (aq), we can obtain E g/Ag - Electron solvation energy is neglected in this definition. 

These definitions are interpreted as follows environment atoms recognize the average weighted states of the ligands each ligand recognizes only the environment atoms and itself with the full scale for estimation of its effective Bom radius. Alternate definitions of the electrostatic solvation energy and the effective Bom radius at the intermediate states are also possible.81... 

The article is organized as follows in Section 2, a general discussion concerning the definition of electrostatic potentials in the frame of DFT is presented. In Section 3, the solvation energy is reformulated from a model based on isoelectronic processes at nucleus. The variational formulation of the insertion energy naturally leads to an energy functional, which is expressed in terms of the variation of the electron density with respect to... 

S, I) are more polarizable (they are further away from the nucleus), and since larger soft species have, in general, lower solvation energies, they are better nucleophiles as compared to smaller hard species. (For definition of the term hard and soft nucleophiles, see Box 13.1.) Thus, we can qualitatively understand why, for example, nucleophilicity increases from F to Cl to Br to V (Table 13.3), and why HS- is a stronger nucleophile than OH". 

The atomic radii may be further refined to improve the agreement between experimental and theoretical solvation free energies. Work on this direction has been done by Luque and Orozco (see [66] and references cited therein) while Barone et al. [67] defined a set of rules to estimate atomic radii. Further discussion on this point can be found in the review by Tomasi and co-workers [15], It must be noted that the parameterization of atomic radii on the basis of a good experiment-theory agreement of solvation energies is problematic because of the difficulty to separate electrostatic and non-electrostatic terms. The comparison of continuum calculations with statistical simulations provides another way to check the validity of cavity definition. A comparison between continuum and classical Monte Carlo simulations was reported by Costa-Cabral et al. [68] in the early 1980s and more recently, molecular dynamics simulations using combined quantum mechanics and molecular mechanics (QM/MM) force-fields have been carried out to analyze the case of water molecule in liquid water [69],... 

An important factor to be considered is the computational cost. Continuum methods are noticeably less expensive than simulation methods based on discrete models. On the other hand, simple properties, as the solvation energy AGso of small and medium-size solutes are computed equally well with both continuum and discrete methods, reaching chemical accuracy (Orozco et al., 1992 Tomasi, 1994 Cramer and Truhlar, 1995a). There is large numerical evidence ensuring that the same conclusion holds for other continuum and discrete methods as well. The evaluation of A(jso at TS has given almost identical results in several cases, but here numerical evidence is not sufficient to draw definitive conclusions. 

From the definition of acidity in solution as presented in Eq. (7.4), it is clear that in order to compute AG° one must know the proton solvation energy. However, from the previous discussion on the structural models for the hydrated proton one may anticipate some difficulties. For example, how many water molecules should be considered in the calculation of the proton solvation energy In other words How large should one take the H (H20) cluster One reasonable approach should be to examine the convergence of... 

In some circunstances, it might be convenient to take the hydronium ion as the basic unit for a proton in solution. In those cases, what is needed is the hydronium solvation free energy, AG° i (HgO ). Table VII.IO shows the results of theoretical calculations (da Silva [44b]), unless otherwise speci-hed) obtained with different continuum solvation models, according to the Ben-Naim [106] definition of the solvation process. Note that the only experimental value available (Pearson [107]) was obtained assuming AG/oi (H ) = —259.5 kcal/mol, which differs considerable from the more recent experiments of Tissandier et al. [104]. However, if one adopts Tissandier s result for the proton solvation energy, Pearson s scheme furnishes AG/oi (H30 ) = —106.16 kcal/mol, a value in close agreement with some of the theoretical results shown in Table VII.IO. 

---