Theory and molecular dynamics simulations of intrinsic localized modes and defect formation in solids

Abstract

Molecular dynamics (MD) simulations of recoil processes following the scattering of x-rays or neutrons have been performed in ionic crystals and metals. At small energies (< 10 eV) the recoil can induce intrinsic localized modes (ILMs) and linear local modes associated with these modes. As a rule, the frequencies of such modes are located in the gaps of the phonon spectrum. However, in metallic Ni, Nb and Fe, due to the renormalization of atomic interactions by free electrons, the frequencies mentioned are found to be positioned above the phonon spectrum. It has been shown that these ILMs are highly mobile and can efficiently transfer a concentrated vibrational energy over large distances along crystallographic directions. If the recoil energy exceeds tens of eVs, vacancies and interstitials can be formed, which are strongly dependent on the direction of the recoil momentum. In NaCl-type lattices the recoil in (110) direction can produce a vacancy and a crowdion, while in the case of a recoil in (100) and in (111) directions a bi-vacancy and a crowdion can be formed.