Charge Transport: Paths and Energy Profiles

To maintain life, charge transfer processes must be efficient to allow electrons to migrate across distances as large as 30 – 50 Å within a timescale from picoseconds to milliseconds, and the free-energy cost should not exceed one electron volt. By employing local ionization and local affinity energies, we calculated the pathway for electron and electron-hole transport, respectively. The pathway is then used to calculate both the driving force and the activation energy. The electronic coupling is calculated using configuration interaction procedure. When the charge acceptor is not known, as in oxidative stress, the charge transport terminals is found using Monte-Carlo simulation. These parameters were used to calculate the rate of electron transport described by Marcus theory. Applying this approach to electron transport in azurin and hole-hopping in cytochrome c peroxidase gave an effective method to calculate the charge transport pathways and the free-energy profiles within 0.1 eV and electronic coupling within 3 meV from the experimental measurements.