Structural evolution in liquid calcium under pressure

Abstract

The atomic structure evolution of liquid Ca at 3500K as a function of pressure up to 100GPa has been studied by ab initio molecular dynamics simulations. The pair correlation function, structure factor and respective peak positions reveal two crossovers at ~10GPa and ~50GPa in liquid Ca while the coordination number shows four pressure regions: about 0.1–5GPa, about 5–20GPa, about 20–50GPa and above ~50GPa and heat capacity shows two different pressure dependences separated at about 30GPa, i.e., below about 30GPa a negative one and a positive value above about 30GPa. It is also observed below 10GPa the first nearest neighbor CaCa distance decreases more sharply as compared to above 10GPa, this behavior is attributed to the gradual occupation of the interstitial sites. Comparisons of the pressure-dependent bond angle distribution and bond orientation order data of liquid Ca with solid crystalline phases imply that pressure-dependent atomic structural evolution in liquid calcium is, to some extent, similar to that of solid crystalline calcium reported by Teweldeberhan and Bonev [Phys. Rev. B 78 140101(R) (2008)]. These sluggish structural crossovers that have been observed in liquid Ca under pressure will trigger more studies in other disordered systems.