Short range orders in molten Al: An ab initio molecular dynamics study

Short range orders (SROs) in molten Al from 943 to 1523 K have been studied through ab initio molecular dynamics simulations. Pair-correlation functions, bond-angle distribution functions, Honeycutt and Andersen analysis were employed to study the local structure of molten Al. A set of indices (l2,l3,l4…lj) were defined to differentiate the SROs. FCC- and HCP-SROs do not exist in equilibrium molten Al generally. Small amount of icosahedral or icosahedron-like SROs are found in molten Al and the structures of the most SROs are more complex than an icosahedron. The non-monotonous or non-classical evolution for the amount of the specific SROs, with five and six 15xx + 1431 (sum of 15xx and 1431) bonded-pairs packing around the central atom, induce that the evolution of self-diffusion constants obeys different Arrhenius relationships in temperature ranges lower and higher than 1073 K.