Determination of the pressure dependent melting temperatures of Al and Ni using molecular dynamics

We present the results of a molecular dynamics simulation study designed to calculate the melting temperatures of pure nickel and pure aluminum at various system pressures using an embedded atom method type potential. The melting points are determined using a two-phase coexistence method, where the liquid and solid phases are modeled simultaneously at a fixed pressure and temperature, allowing us to bracket the value within a desired range of accuracy. The values obtained for the melting points of aluminum are consistently higher than expected based on experiment, while those for nickel are lower. Other thermal properties of aluminum and nickel were determined in order to fit the melting temperature data into a standard theoretical framework. Also, planar material defects, such as twin boundaries and stacking faults, were observed in crystals grown from the melt, occurring more often in aluminum systems than in nickel. Planar defect energies were calculated for both systems in order to explain these observations.