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.
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