This proposal describes theoretical studies of model porphyrin compounds and of the photosynthetic reaction center. The emphasis is on large scale ab initio electronic structure calculations for these systems using novel numerical techniques developed during the previous granting period which greatly reduce the computational effort needed to carry out high quality ab initio calculations for molecules containing 20-200 atoms. We will determine ground and excited state energies, redox potentials, equilibrium geometries, force fields, charge distributions, dispersion interactions, and-intermolecular electronic couplings for a wide variety of porphyrin moieties, including bacteriochlorophylls embedded in the reaction center protein environment. This information will then be used to calculate optical spectra and electron transfer dynamics in the photosynthetic reaction center, using theoretical methods for spectroscopic and quantum molecular dynamics simulations that we have developed over the past 10 years. We have proposed a simple physical model which explains the efficiency of charge separation in the reaction center and agrees qualitatively with the existing experimental data. The microscopic simulations described above will allow more quantitative models to be constructed, and will permit confirmation (or contradiction) of the basic picture that we have assembled on the basis of phenomenological modeling.
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