This variable defines the factor between the timescale of photonic
and electronic movement.
for more details see the documentation of TDIonicTimeScale
If you also use TDIonicTimeScale, we advise to set
TDPhotonicTimeScale = TDIonicTimeScale, in the case the
photon frequency is in a vibrational energy range.
Important: The electronic time step will be the value of
TDTimeStep divided by this variable, so if you have determined an
optimal electronic time step (that we can call dte), it is
recommended that you define your time step as:
TDTimeStep = dte * TDPhotonicTimeScale
so you will always use the optimal electronic time step