Dynamics of primary charge separation in bacterial photosynthesis using the multilevel Redfield-Davies secular approach

We use Redfield's relaxation theory in the Davies formulation to study primary charge separation reactions in bacterial photosynthesis. The specific model studied is the standard one (spin-boson), with three states for the system, harmonic oscillators for the bath, and linear ohmic system-bath coupling. The Redfield-Davies formulation, which is equivalent to the secular approximation, is Markovian, of second order in system-bath coupling, and is written for the system's density matrix. The approximation does not suffer from any negative probabilities (which appear in the original Redfield approach) and can therefore be used for long-time processes (20 ps or more here). Our results are in line with previous studies, especially to high bath frequencies. They confirm the usefulness of the Redfield-Davies secular approach as a convenient and simple tool for studying system-bath processes.