  In this letter we explore how the microscopic dynamics of charge transfer
(CT) excitons are influenced by the presence of an external magnetic field in
disordered molecular semiconductors. This influence is driven by the dynamic
interplay between the spin and spatial degrees of freedom of the electron-hole
pair. To account for this interplay we have developed a numerical framework
that combines a traditional model of quantum spin dynamics with a
coarse-grained model of stochastic charge transport. This combination provides
a general and efficient methodology for simulating the effects of magnetic
field on CT state dynamics, therefore providing a basis for revealing the
microscopic origin of experimentally observed magnetic field effects. We
demonstrate that simulations carried out on our model are capable of
reproducing experimental results as well as generating theoretical predictions
related to the efficiency of organic electronic materials.
