It is very important to choose correctly the time step of a simulation. This is a very important topic of a simulation. This have to be done in a very accurate manner, in order to avoid unphysical phenomena like strange oscillations in electric field or too much scattering effects and so on... Actually, algorithm based on the plasma oscillations of a gas of charged particles exists which are usefull in the choice of a correct time step. This is not implemented, at the moment, so the user have to specify it. This is done in the following fashion. For example, if the user wants to set the time step to 0.01 picoseconds, the following command line in the input file is needed
TIMESTEP 0.01e-12