INFLUENCE OF THE INTERATOMIC POTENTIAL ON THE STRUCTURE OF DISLOCATIONS IN A MONOLAYER

Using atomic relaxation techniques, dislocation dipoles of various siz es and orientations have been studied for monolayers with the Lennard- Jones potential (LJP) and nearest-neighbour piecewise linear force (PL F) interactions. In the LJP system the lower energy vacancy dipoles ha ve over a wide range of angles an energy which is mainly a function of the vacancy content of the dipole. There is a competition between the elastic forces and the topological constraints which favour a five-fo ld coordinate vacancy (FCV) at the centre of each core. For the short range PLF system the lattice usually compresses upon the introduction of a dislocation, a consequence of the soft core of the interaction po tential, and interstitial dipoles are lower in energy. For the long ra nge LJP system the dislocations are mobile whereas for the PLF system they are pinned. The relevance of these results to existing theories o f melting are discussed.