Molecular dynamics simulation of the homogeneous crystallization of liquid rubidium

The homogeneous crystallization of liquid rubidium models containing 500, 998, and 1968 particles in the basic cube was studied by the molecular dynamics method. The liquid crystallized over the temperature range 70–182.5 K predominantly with the formation of a body centered cubic (BCC) structure. The mechanism of crystallization was different from that accepted in classic nucleation theory. Crystallization developed as an increase in the number of atoms with Voronoi polyhedra of the 0-6-0-8 and 0-4-4-6 types, the formation of bound groups (clusters) from these atoms, and growth of these groups as in the coagulation of an impurity from a supersaturated solution. At the initial stage, bound groups had a very loose structure and included a fairly large number of atoms with polyhedra of other types. The linear dimension of the largest group rapidly approached the basic cube size. The atoms with the 0-6-0-8 and 0-4-4-6 Voronoi polyhedra played a leading role in crystallization and activated the transition of bound group atoms with other coordination types into a BCC coordination. The probability of formation of a bound group of a given size was found to be independent of the volume of the liquid model. Cluster size fluctuations especially strong over the temperature range 180–185 K played an important role in the formation of 0608 clusters of a threshold (“critical”) size.