  Computation of collisional energy loss in a finite size QCD medium has become
crucial to obtain reliable predictions for jet quenching in ultra-relativistic
heavy ion collisions. We here compute this energy loss up to the zeroth order
in opacity. Our approach consistently treats both soft and hard contributions
to the collisional energy loss. Consequently, it removes the unphysical energy
gain in a region of lower momenta obtained by previous computations. Most
importantly, we show that for characteristic QCD medium scales, finite size
effects on the collisional energy loss are not significant.
