Ab initio molecular dynamics study of the structure of undercooled Ni melt

The structure of undercooled Ni melt was studied by ab initio molecular dynamics simulations. “Cage effect” is obvious based on the calculated normalized velocity autocorrelation functions and will be enhanced with a decrease in temperature. It is found that the fractions of 1661-, 1551- and 1441-type bonded-pairs increase with the decrease in temperature and all the others decline. The fractions and lifetimes of the Voronoi clusters were calculated. The existence of icosahedral short-range orders is confirmed. The icosahedral cluster has the longest average lifetime, however, it is not the most abundant one. The most abundant cluster is the one with Voronoi cell index of <0,4,8,1>. The average lifetime of all clusters increases with a decrease in temperature.