Molecular dynamics simulations of the melting curves and nucleation of nickel under pressure

Three embedded atom method potentials have been applied to investigate the melting properties of nickel under compression. In these three potentials, Mendelev's potential can reproduce a satisfying melting curve, which accords well with the experiments and first-principles calculations. Thus, we recommend that the Mendelev's potential should be a reliable potential for simulating melting properties of nickel. Using Mendelev's potential, we calculated the melting of Ni with two approaches, i.e., hysteresis approach and two-phase method. Both approaches produce results in very close proximity, with the disagreement less than 4.35% at the applied pressures. Fitting the well-known Simon equation to our melting data yields the melting curves for Ni: 1651(1+P/35.172)^0.607 (hysteresis approach) and 1725(1+P/39.812)^0.617 (two-phase approach). Based on the hysteresis method, we investigated in detail the melting nucleation of nickel at high pressure, and found that with pressure increasing, the critical nucleus size r^⁎ increases fast first and then decreases, and again rises. When taking account of the Gibbs free energy barrier ΔG^⁎, it found that the ΔG^⁎ increase monotonically with pressure up to 300 GPa, and can be described as a third-order polynomial relation