  The recently introduced method of excess collisions (MEC) is modified to
estimate diffusion-controlled reaction times inside systems of arbitrary size.
The resulting MEC-E equations contain a set of empirical parameters, which have
to be calibrated in numerical simulations inside a test system of moderate
size. Once this is done, reaction times of systems of arbitrary dimensions are
derived by extrapolation, with an accuracy of 10 to 15 percent. The achieved
speed up, when compared to explicit simulations of the reaction process, is
increasing proportional to the extrapolated volume of the cell.
