COLLISION CASCADES IN CU, AU AND CU3AU - A COMPARISON BETWEEN MOLECULAR-DYNAMICS AND THE BINARY COLLISION APPROXIMATION

The mean number of moving atoms in cascades is estimated as a function of time during the first 150 fs of the cascade development in Cu, Au and ordered AuCu3 single crystals. The incident energy of the copper and gold external projectiles ranges from 100 eV to 1 keV. The same simulations are performed both by molecular dynamics and in the binary collision approximation with the MARLOWE program. The models are intentionally made as close as possible in order to test the validity of the binary collision approximation in the cases studied. In general, the results obtained with both programs are in good agreement. The only large relative difference is found for the number of moving gold atoms in AUCU3 in the case of the lowest incident energies. In this case the number of moving gold atoms is found to be up to 50% larger when estimated by molecular dynamics than in the binary collision approximation. This may result from those interactions between moving copper and gold atoms which are not modelled in the binary collision approximation.