Atomistic simulation of dislocations, surfaces and interfaces in MgO

A new simulation code for modelling extended defects e.g. linear (dislocations) and planar (surfaces and grain boundaries) at the atomistic level is introduced. One of the key components is the ability to calculate the Coulombic potential of a solid with one-dimensional periodicity. This approach has been applied to screw dislocations in MgO and we have evaluated the structure (including core size) and stability of the [100] and 1/2[110] screw dislocations. The 1/2[110] dislocation, which has the shortest Burgers vector, was found to be more stable, as predicted by elasticity theory, although the simulations show that elasticity theory underestimates the energy difference. In addition, it has been shown that by using this new computer simulation code METADISE, following the approach of Tasker, the structure and energetics of surfaces and interfaces can be calculated. This method has been applied to modelling micro-faceting and it was found that micro-facetted {110} and {111} surfaces of MgO are the most stable forms of these surfaces. The formation energy of tilt grain boundaries in MgO ({h10} and {h20}) as a function of misorientation angle was also investigated and it was found that for the {h10} series the formation energy is proportional to the interfacial bond density while no such pattern can be found for the {h20} series.