Structural motifs and stability of small argon–nitrogen clusters

Abstract

The molecular dynamics (MD) simulation method is used to study Arm(N2)n clusters. Using realistic pair potentials for the argon–argon, nitrogen–nitrogen, and argon–nitrogen interactions, the structures and thermodynamics of these clusters are investigated. The initial focus of the study is the series of thirteen particle clusters of Arm(N2)13−m (0⩽m⩽13). These icosahedral argon–nitrogen clusters display systematic changes in energetics when argon is substituted by nitrogen in the central position. The relative stability of argon-centered clusters over nitrogen-centered clusters is further investigated by defining and calculating a “species-centric” order parameter which can be monitored during a MD simulation. These results are interpreted in terms of frustration effects due to anisotropy in the N2–N2 and N2–Ar potentials. The consequences of these observations for cluster stability and for dynamical behavior, such as melting and evaporation, are investigated. The dynamical studies of larger clusters reveal that the mixed clusters evolve towards a structure with an argon core coated by a nitrogen shell.