Modeling of self-localized vibrations and defect formation in solids

MD simulations of recoil processes, following the scattering of X-rays or neutrons are performed. At small energies (<10 eV) the recoil can induce intrinsic localized modes and linear local modes associated with them. In ionic crystals the frequencies of these modes are located in the gaps of the phonon spectrum, being essentially dependent on long-range forces. In metals, as a result of the screening of atomic interactions by free electrons, their frequencies can be positioned above the phonon spectrum. The MD simulations of vibrations in Ni and Nb confirm this prediction. If the recoil energy exceeds tens of eV, the vacancies and interstitials can be formed. In fcc lattices a recoil in (1 1 0) direction can produce a vacancy and a crowdion, while in the case of a recoil in (1 0 0) and in (1 1 1) directions a bi-vacancy and a crowdion can be formed.