Ab initio molecular dynamics simulations of low energy recoil events in ceramics

The recent progress in the use of large-scale ab initio molecular dynamics (AIMD) to investigate low energy recoil events and determine threshold displacement energies, E-d, in ceramics is reviewed. In general, E-d shows a significant dependence on recoil direction and atom. In 3C-SiC, the minimum E-d for both C and Si atoms is found along the < 1 0 0 > direction, with a value of 20 and 49 eV, respectively. The results demonstrate that significant charge transfer occurs during the dynamics process, and defects can enhance charge transfer to surrounding atoms, which provides important insights into the formation of charged defects. It is found that the C vacancy is a positively charged defect, whereas the Si vacancy is in its neutral state. The minimum E-d in GaN is determined to be 17 and 39 eV for N and Ga atoms, respectively, both along the <(1) over bar 0 1 0 > direction. The average E-d for N atoms (32.4 eV) is smaller than that for Ga atoms (73.2 eV). It is of interest to note that the N defects created along different crystallographic directions have a similar configuration (a N-N dumbbell configuration), but various configurations for Ga defects are formed. In Y2Ti2O7 prochlore, the minimum E-d for Y atoms is determined to be 27 eV for a recoil along the < 1 0 0 > direction, 31.5 eV for Ti atoms along the < 1 0 0 > direction, 14.5 eV for O-48f atoms along the < 1 1 0 > direction and 13 eV for O-gb atoms along the < 1 1 1 > direction. The average E-d values determined are 32.7, 34.2, 14.2 and 16.1 eV for yttrium, titanium, O-48f and O-gb atoms, respectively. (C) 2011 Elsevier B.V. All rights reserved.