Relation between the interaction potential, replacement collision sequences, and collision cascade expansion in iron

Abstract

The binary collision approximation ͑BCA͒ grounded on molecular dynamics results is used to investigate the influence of the range and stiffness of interatomic potentials on the replacement collision sequence ͑RCS͒ length and frequency distributions as well as on the displacement cascade expansion and density. Different screened Coulomb potential functions are used in the Marlowe BCA program with suitably adjusted screening lengths. We show in this paper that for screened Coulomb potentials, the shorter the range, the lower the focusing threshold and the more important the RCS production. The cascade expansion and density is quite sensitive to the potential range at high interaction energies. The overall cascade expansion is found to be governed by the 10% highest-energy recoils. Their energy is above the RCS focusing energy threshold. The cascade density, i.e., the number of transient defects produced per unit volume, is suggested sufficient to interfere significantly with RCS propagation and thus with the spatial distribution of Frenkel pairs. Primary damage production thus involves the combined effect of high-energy collisions and RCS production. A careful choice of the short range potential has thus to be made when simulating displacement cascades.

Effect of the interatomic potential on the features of displacement cascades in α-Fe: A molecular dynamics study

“…characterised by a high S/R ratio) favour the process of energy transfer during the binary collision, thereby favouring the production of more, and longer, RCS [44]. Clearly, this mechanism of defect production favours the spreading of the cascade over large volumes and penalises defect recombination.…”

“…These magnitudes have been introduced in Ref. [44] to describe the behaviour of the potential in the intermediate interval of interatomic distances, where the transition between near-equilibrium atomic oscillations and highenergy regime occurs. In this interval, the manybody potentials used for MD simulations of cascades are typically joined to a high-energy pair potential, more appropriate to describe collisions at close distances (stiffening of the potential, see e.g.…”

“…It can be seen that, although eventually, for high enough energies, all curves join the ZBL, the way the connection is made can greatly differ in the intermediate energy and distance region, thereby leading to possible differences in the cascade outcome. In particular, the parameters R and S have been shown, in a binary collision approximation (BCA) study [44], to correlate with the number of replacement collision sequences (RCS) of the cascade. In addition, the stiffness at higher energies ($200 eV), here denoted as U, has been seen to influence the cascade density [44].…”

“…In particular, the parameters R and S have been shown, in a binary collision approximation (BCA) study [44], to correlate with the number of replacement collision sequences (RCS) of the cascade. In addition, the stiffness at higher energies ($200 eV), here denoted as U, has been seen to influence the cascade density [44]. This BCA study suggests therefore that the features of the function chosen to stiffen the potential may have an important role on the outcome of the cascade.…”

Relevancy of displacement cascades features to the long term point defect cluster growth

“…This recombination radius was adjusted so as to predict the same number of Frenkel pairs (FP) as full MD [4]. The validity and limits of this method are extensively discussed in the literature [4,[8][9][10][18][19][20][21][22][23][24].…”