Comparison of molecular dynamics and binary collision approximation simulations for atom displacement analysis

Molecular dynamics (MD) and binary collision approximation (BCA) computer simulations are employed to study surface damage by single ion impacts. The predictions of BCA and MD simulations of displacement cascades in amorphous and crystalline silicon and BCC tungsten by 1 keV Ar++ ion bombardment are compared. Single ion impacts are studied at angles of 50°, 60° and 80° from normal incidence. Four parameters for BCA simulations have been optimized to obtain the best agreement of the results with MD. For the conditions reported here, BCA agrees with MD simulation results at displacements larger than 5 Å for amorphous Si, whereas at small displacements a difference between BCA and MD arises due to a material flow component observed in MD simulations but absent from a regular BCA approach due to the algorithm limitations. MD and BCA simulation results for crystalline W are found to be in a good agreement even at small displacements, while in crystalline Si there is some difference due to displacements in amorphous pockets.