  We present a highly efficient molecular dynamics scheme for calculating the
concentration depth profile of dopants in ion irradiated materials. The scheme
incorporates several methods for reducing the computational overhead, plus a
rare event algorithm that allows statistically reliable results to be obtained
over a range of several orders of magnitude in the dopant concentration.
  We give examples of using this scheme for calculating concentration profiles
of dopants in crystalline silicon. Here we can predict the experimental profile
over five orders of magnitude for both channeling and non-channeling implants
at energies up to 100s of keV.
  The scheme has advantages over binary collision approximation (BCA)
simulations, in that it does not rely on a large set of empirically fitted
parameters. Although our scheme has a greater computational overhead than the
BCA, it is far superior in the low ion energy regime, where the BCA scheme
becomes invalid.
