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Anharmonicity solvent effects

Amides, alkaline hydrolysis, 215 Anharmonic systems, direct evaluation of quantum time-correlation functions, 93 Apollo DSP—160, CHARMM performance, 129/ simulations, solvent effects, 83... [Pg.423]

The force controls the remarkably persistent coherence in products, a feature that was unexpected, especially in view of the fact that all trajectory calculations are normally averaged (by Monte Carlo methods) without such coherences. Only recently has theory addressed this point and emphasized the importance of the transverse force, that is, the degree of anharmonicity perpendicular to the reaction coordinate. The same type of coherence along the reaction coordinate, first observed in 1987 by our group, was found for reactions in solutions, in clusters, and in solids, offering a new opportunity for examining solvent effects on reaction dynamics in the transition-state region. [Pg.25]

In our discussion the usual Born-Oppenheimer (BO) approximation will be employed. This means that we assume a standard partition of the effective Hamiltonian into an electronic and a nuclear part, as well as the factorization of the solute wavefunction into an electronic and a nuclear component. As will be clear soon, the corresponding electronic problem is the main source of specificities of QM continuum models, due to the nonlinearity of the effective electronic Hamiltonian of the solute. The QM nuclear problem, whose solution gives information on solvent effects on the nuclear structure (geometry) and properties, has less specific aspects, with respect the case of the isolated molecules. In fact, once the proper potential energy surfaces are obtained from the solution of the electronic problem, such a problem can be solved using the standard methods and approximations (mechanical harmonicity, and anharmonicity of various order) used for isolated molecules. The QM nuclear problem is mainly connected with the vibrational properties of the nuclei and the corresponding spectroscopic observables, and it will be considered in more detail in the contributions in the book dedicated to the vibrational spectroscopies (IR/Raman). This contribution will be focused on the QM electronic problem. [Pg.82]

Thus, significant improvements of calculated rotational strengths await the incorporation of anharmonicity and solvent effects and the development of superior functionals. In the meantime, it is clear that the current DFT/GIAO methodology is of very high... [Pg.201]

Figure 17 Schematic illustration of the viscoelastic (VE) model of dephasing. The vibrating molecule (toluene here) occupies a cavity within the solvent with a certain size in v = 0. In v = 1, the radius of the cavity is slightly larger, because of vibrational anharmonicity. This effect couples shear fluctuations of the solvent to the vibrational frequency. See also Fig. 18. [Pg.433]

As a numerical example, we investigate ET in the Marcus inverted regime to reveal the solvent effect. The potentials in the fast q) and slow (x) coordinates are modeled by two shifted harmonic oscillators, although the approaches can be straightforwardly applied to anharmonic systems. The parameters. [Pg.321]

Supplementing this equation with an additional set of solvent oscillators one can incorporate a solvent environment. Notice that this does not necessarily imply harmonic solvent motions. In fact the full anharmonicity of the solvent can be accounted for in the context of linear response theory [39] where the interaction is described in terms of an effective harmonic oscillator bath. This allows calculation of relaxation rates from classical molecular dynamics simulations of the force fn(x) exerted by the solvent on the relevant system. This approach has found appli-... [Pg.82]


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See also in sourсe #XX -- [ Pg.342 ]




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