Quantum Biodynamics

We explore the dynamics of light-induced charge transfer in chemical structures.The spatio-temporal carrier dynamics in optically excited light-harvesting molecular ensembles is investigated on the basis of a drift-diffusion model. The equations of motion include the local excitation of the molecular ensemble and the spatio-temporal dynamics of carriers and currents.   

We refer to a threedimensional area that is filled with (oriented) molecules. The system is connected to two electrodes and embedded in an electric circuit. The chemical ensemble may be optically excited at a (generally arbitrary) spatial area within the probe. In our example we consider a light beam of circular cross section that is injected in the centre of the probe (perpendicular to the z-direction).

Our space-time simulation combines various levels of approaches:

• On the first level, we calculate (in each grid point of our threedimensional probe) the  probabilities for an occupation of the molecular levels i.e. the ground state and excited states via a rate equation approach. This allows the spatially dependent calculation of the local carrier generation (which we assume to be proportional to the density of molecules in the excited states).

• On the second level, we use a drift-diffusion equation to model the carrier distribution and current flow at each spatial point of the system. The two levels of approaches are coupled via the rate of local carrier generation.
  The properties of the molecular system are considered via a multi-level structure and a parameter set of rates coupling the occupation in the various levels.
  

  Simulations reveal the dynamics of the photo-induced current after optical excitation and allows to visualize the temporal behaviour of the molecular occupation. The excitation and relaxation dynamics within the molecular ensemble thereby shows a strong dependence on molecular parameters and initialisation.