  The Frenkel-Kontorova chain with a free end is used to study initiation and
propagation of crowdions (anti-kinks) caused by impact of a molecule consisting
of K atoms. It is found that molecules with 1 < K < 10 are more efficient in
initiation of crowdions as compared to single atom (K = 1) because total energy
needed to initiate the crowdions by molecules is smaller. This happens because
single atom can initiate in the chain only sharp, fast-moving crowdions that
requires a relatively large energy. Molecule has finite length, that is why it
is able to excite a wider crowdion with a smaller velocity and smaller energy.
Our results can shed light on the atomistic mechanisms of mass transfer in
crystals subject to atom and molecule bombardment.
