Polarizable continuum

Mineva T, Russo N and Sicilia E 1998 Solvation effects on reaction profiles by the polarizable continuum model coupled with Gaussian density functional method J. Oomp. Ohem. 19 290-9... 

T. A. Keith and M. J. Frisch, A Fully Self-Consistent Polarizable Continuum Model of Solvation with Analytic Energy Gradients, in preparation (1996). 

The Polarizable Continuum Model (PCM) employs a van der Waals surface type cavity, a detailed description of the electrostatic potential, and parameterizes the cavity/ dispersion contributions based on the surface area. The COnductor-like Screening... 

Barone, V. Cossi, M. Tomasi, J. A new definition of cavities for the computation of solvation free energies by the polarizable continuum model. J. Chem. Phys. 1997, 107, 3210-3221. 

As can be seen from the histogram in Figure l-l(b), the loose conformation is preferred over the tight one, a result only possible with inclusion of solvent effects. Ab-initio calculations of those conformers show that, without the inclusion of solvent effects, the tight conformer is preferred by 7.4 kcal/mol, while the inclusion of solvent effects (with polarizable continuum model, PCM) shifts the preference towards the loose conformer, which becomes more stable than the tight one by 0.1 kcal/mol. 

Fig. 2.2 Self-Consistent Reaction Field (SCRF) model for the inclusion of solvent effects in semi-empirical calculations. The solvent is represented as an isotropic, polarizable continuum of macroscopic dielectric e. The solute occupies a spherical cavity of radius ru, and has a dipole moment of p,o. The molecular dipole induces an opposing dipole in the solvent medium, the magnitude of which is dependent on e.

Fortunelli, A. and J. Tomasi. 1994. The implementation of density functional theory within the polarizable continuum model for solvation. Chem. Phys. Lett. 231, 34. 

In the IPCM calculations, the molecule is contained inside a cavity within the polarizable continuum, the size of which is determined by a suitable computed isodensity surface. The size of this cavity corresponds to the molecular volume allowing a simple, yet effective evaluation of the molecular activation volume, which is not based on semi-empirical models, but also does not allow a direct comparison with experimental data as the second solvation sphere is almost completely absent. The volume difference between the precursor complex Be(H20)4(H20)]2+ and the transition structure [Be(H20)5]2+, viz., —4.5A3, represents the activation volume of the reaction. This value can be compared with the value of —6.1 A3 calculated for the corresponding water exchange reaction around Li+, for which we concluded the operation of a limiting associative mechanism. In the present case, both the nature of [Be(H20)5]2+ and the activation volume clearly indicate the operation of an associative interchange mechanism (156). 

J. L. Rivail and D. Rinaldi, Liquid state quantum chemistry computational applications of the polarizable continuum models, in Computational Chemistry, Review of Current Trends, J. Leszczynski, ed., World Scientific, New York (1996) pp. 139-174. 

C. Amovilli, V. Barone, R. Cammi, E. Cancfes, M. Cossi, B. Menucci, C. S. Pomelli, and J. Tomasi, Recent advances in the description of solvent effects with the polarizable continuum model, Adv. Quantum Chem. 32 227 (1998). 

The most common approach to solvation studies using an implicit solvent is to add a self-consistent reaction field (SCRF) term to an ab initio (or semi-empirical) calculation. One of the problems with SCRF methods is the number of different possible approaches. Orozco and Luque28 and Colominas et al27 found that 6-31G ab initio calculations with the polarizable continuum model (PCM) method of Miertius, Scrocco, and Tomasi (referred to in these papers as the MST method)45 gave results in reasonable agreement with the MD-FEP results, but the AM1-AMSOL method differed by a number of kJ/mol, and sometimes gave qualitatively wrong results. 

Fig. 8. Energies calculated with a polarizable continuum model, differences of the sums of all metal-oxygen bond lengths, AS(M-O), and energy profiles for water exchange on rhodium(III) and ruthenium(II) hexaaqua ions.

These problems were partially solved through the inclusion of multipole expansions in ellipsoidal cavities [23] or through the use of the polarizable continuum method... 

Tomasi, J., Bonaccorsi, R., Cammi, R. and Olivares del Valle, F. J. Theoretical chemistry in solution. Some results and perspectives of the continuum methods and in particular of the polarizable continuum model,. J.Mol.Struct., 234 (1991), 401-424... 

In addition to these external electric or magnetic field as a perturbation parameter, solvents can be another option. Solvents having different dielectric constants would mimic different field strengths. In the recent past, several solvent models have been used to understand the reactivity of chemical species [55,56]. The well-acclaimed review article on solvent effects can be exploited in this regard [57]. Different solvent models such as conductor-like screening model (COSMO), polarizable continuum model (PCM), effective fragment potential (EFP) model with mostly water as a solvent have been used in the above studies. 

The elucidation of actinide chemistry in solution is important for understanding actinide separation and for predicting actinide transport in the environment, particularly with respect to the safety of nuclear waste disposal.72,73 The uranyl CO + ion, for example, has received considerable interest because of its importance for environmental issues and its role as a computational benchmark system for higher actinides. Direct structural information on the coordination of uranyl in aqueous solution has been obtained mainly by extended X-ray absorption fine structure (EXAFS) measurements,74-76 whereas X-ray scattering studies of uranium and actinide solutions are more rare.77 Various ab initio studies of uranyl and related molecules, with a polarizable continuum model to mimic the solvent environment and/or a number of explicit water molecules, have been performed.78-82 We have performed a structural investigation of the carbonate system of dioxouranyl (VI) and (V), [U02(C03)3]4- and [U02(C03)3]5- in water.83 This study showed that only minor geometrical rearrangements occur upon the one-electron reduction of [U02(C03)3]4- to [U02(C03)3]5-, which supports the reversibility of this reduction. 

It is relatively straightforward to implement the polarizable continuum model (PCM) via Eq. (39).11 12,105,117 The potential of the reaction field, VCT(r), is due to the ostensible (virtual) charge distribution o(r) on the cavity surface, which in turn is related to the potential Vsoiutc(r) that arises from the nuclei and electrons of the solute molecule, Eq. (2). Since the latter is likely to be further polarized by VCT(r), thus affecting Vs0,utc(r), iteration to self-consistency is needed,105,106 as already has been pointed out. (However Montagnani and Tomasi suggest that this often has little practical consequence.)118... 

Application of CBS extrapolations to the A5-ketosteroid isomerase-catalyzed conversion of A5-androstene-3,17-dione to the A4 isomer (Fig. 4.10) provides a test case for extensions to enzyme kinetics. This task requires integration of CBS extrapolations into multilayer ONIOM calculations [56, 57] of the steroid and the active site combined with a polarizable continuum model (PCM) treatment of bulk dielectric effects [58-60], The goal is to reliably predict absolute rates of enzyme-catalyzed reactions within an order of magnitude, in order to verify or disprove a proposed mechanism. 

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