Complex systems electrostatic energy

A. rather complex procedure is used to determine the Born radii a values of which. calculated for each atom in the molecule that carries a charge or a partial charge. T Born radius of an afom (more correctly considered to be an effective Born radii corresponds to the radius that would return the electrostatic energy of the system accordi to the Bom equation if all other atoms in the molecule were uncharged (i.e. if the other ato only acted to define the dielectric boundary between the solute and the solvent). In Sti force field implementation, atomic radii from the OPLS force field are assigned to ec... 

The result of an energy decomposition analysis performed for this complex was also unusual. In contrast to numerous dihydrogen-bonded systems with significant predominance of the electrostatic interaction, the dihydrogen-bonded dimer (LiH H20)2 has shown the charge transfer contribution to exceed the electrostatic energy —125.30 versus —81.40 kcal/mol, respectively. 

For more complex molecules a reasonable estimate of the heat of sorption can sometimes be made by considering group contributions. Such an approach works best for nonpolar sorbates on nonpolar surfaces but is subject to considerable error for polar systems in which the electrostatic energies of adsorption are large. 

Frontera and Deyii [38] warn that although it is true that the interaction energies of benzene with cations and hexafluorobenzene with anions are similar, it is not possible to generalize that the interaction energies calculated for the anion-n complexes are comparable to those obtained for the cation-7T complexes. These authors also indicate that the same is apphcable to Kim s conclusion stating that the largest contribution in anion-n complexes are electrostatic and induction, because as we have seen before, these contributions sharply depend of the Qzz and a values of the aromatic system. 

Numerically, it is now a common practice to calculate within the dielectric continuum formulation but employing cavities of realistic molecular shape determined by the van der Waals surface of the solute. The method is based upon finite-difference solution of the Poisson-Boltzmann equation for the electrostatic potential with the appropriate boundary conditions [214, 238, 239]. An important outcome of such studies is that even in complex systems there exists a strong linear correlation between the calculated outer-sphere reorganization energy and the inverse donor-acceptor distance, as anticipated by the Marcus formulation (see Fig. 9.6). More... 

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