Improvement of the repulsive part of the classical interatomic potential for SiC

Investigations of ion-beam-induced defect formation by classical molecular dynamics simulations are determined decisively by the quality of the interatomic potentials employed. Potentials of Tersoff and Brenner type are presently considered the best to describe structural and defect properties of SiC. However, their repulsive part does not agree well with state-of-the-art potentials used in atomic collision physics. The subject of the present work is therefore the improvement of the repulsive interaction in the Tersoff and Brenner type potentials, in order to enable a better description of ballistic and athermal processes occuring during ion bombardment of SiC. At small interatomic distances the pair part of these potentials is replaced by the well-tested ZBL potential. An exponential spline function is employed to connect the ZBL potential with the two-body part of the Tersoff or Brenner potential, in the region between some ten and zero eV. The resulting pair potential and its first derivative must be continuous and monotonic over the whole range of repulsive interaction. The improvements introduced are tested by comparing the energies for repulsive interactions in Si-Si, Si-C, and C-C dimers with corresponding results obtained by ab-initio DFT calculations using the DMOL code. The second modification introduced into the Tersoff and Brenner type potentials concerns their three-body part. Its contribution to the total potential is reduced for small interatomic separations at which the interaction between two atoms should be independent of their coordinations to the other neighbor atoms. This is realized in such a manner that the total potential and its derivative remain continuous and monotonic in the region where the reduction of the three-body part is performed.