Structure of nitrogen molecular clusters (N2)n with 13 ≤ n ≤ 55

We investigate the structural properties of nitrogen molecular clusters (N-2)(n), using classical Monte Carlo simulations and optimization methods. As is the case for argon clusters, we find polyicosahedral (anti-Mackay) geometries above 13 molecules, and multilayer icosahedra with uncomplete outer shell (Mackay) geometries below 55 molecules. The crossover point between these two kinds of structures is located near 42 molecules, whereas it is at only 31 for argon. With a simple three-body (Axilrod-Teller) potential added to the standard Lennard-Jones model, we interpret this difference as the result of the strong anisotropy of the molecular potential.