The solvent contribution to the reorganization energy of electron transfer can be estimated from averages of the potential energy gaps between neutral-pair and ion-pair states over an ensemble of structures generated from molecular dynamics simulations. Invoking a Marcus-type two-sphere model for charge separation and recombination in an aqueous environment, we explored the effect of a polarizable force field and noted a strong reduction of (by ) compared to the corresponding value obtained with a standard nonpolarizable force field. Both types of force fields yield values that in agreement with the Marcus theory, vary strictly linearly with the inverse of the donor-acceptor distance; the corresponding slopes translate into appropriate effective optical dielectric constants, for a nonpolarizable and for a polarizable force field. The reduction in the solvent reorganization energy due to a polarizable force field translates into a scaling factor that is essentially independent of the donor-acceptor distance. The corresponding effective optical dielectric constant, , is in excellent agreement with experiment for water.
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American Institute of Physics
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