A hybrid MC–MD calculation study

Abstract

It is widely accepted that the binary collision approximation (BCA) is rather accurate in the high energy regime of a collision cascade while multiple interaction describes better the low energy and post collisional regimes. It will be therefore desirable to determine the grade of accuracy when both regimes are treated by their corresponding approximations in a single case study. A silicon sample self-bombarded by 2.5 keV ions has been studied. First of all, 1000 trajectories have been calculated by means of the molecular dynamic MD-TOPS code in order to have a reasonable statistic. These results will be considered as a reference when comparing with a second set of 1000 trajectories calculated within the BC approximation using the Monte Carlo MC-TOPS code in the 2.5–0.25 keV energy range and resuming the calculation in the low energy regime by MD. Input parameters required by MC calculations, such as the displacement energy, E d, bulk energy, E b, and surface binding energy, U, for silicon have been previously calculated by means of a numerical algorithm, POTDIR, which determines the potential energy variation of the crystalline structure as a function of the position of a probe atom which moves within the solid along a prescribed direction. Special attention is paid to the energy conservation when joining the MC and the MD codes. A variety of results obtained by both methods are compared: sputtering, deposited energy in the solid and energy and angular distributions of both the sputtered and the atoms in solid. From the analysis of this comparison it may be concluded that this hybrid calculation method is indeed accurate.