Monte Carlo simulations of dislocation vector systems with long-range interactions reveal two possible types of phase transitions depending on the core energy of dislocations. For dislocations with a large core energy the melting transition is found to be continuous and due to dislocation unbinding. The Kosterlitz-Thouless theory agrees well with the simulation results. For a small core energy the melting transition is caused by the nucleation of grain boundary loops and is found to be first order. The latter transition may correspond to the previous computer experiments on various atomic systems. In addition to thermodynamic quantities such as the energy and specific heat, microscopic configurations and orientational correlation functions are also calculated.

• Received 18 May 1982

DOI:https://doi.org/10.1103/PhysRevB.26.6239