Application of trajectory surface-hopping techniques for modelling electron-transfer processes in organic systems

Background Traditionally the rates of nonadiabatic electron transfer (ET), k(et), are interpreted using the Fermi golden rule (FGR), i.e. k(et) = (4pi(2)/h)\V-el\(2){FCWD}, where V-el is the electronic coupling and FCWD is the Franck-Condon factor.([1]) Within the context of the FGR, explicit effects of molecular vibrations are ignored. This theory fails to address several important issues concerning ET processes in donor-bridge-acceptor systems, such as which molecular vibrations are responsible for mediating the ET processes, and what effect do bridge and chromophore vibrations have on the magnitude of V-el? Trajectory surface hopping (TSH) is a semiclassical method in which classical trajectories are run, and during the evolution of these trajectories, vertical electronic transitions may occur.([2]) The trajectories, therefore, evolve over multiple potential-energy surfaces. This makes TSH ideal for addressing the above questions. Pioneering TSH models were developed by Tully and Preston,([3]) and Miller and George.([4]) Details of our semiempirical based TSH method are presented elsewhere.([5]).