Conclusion

We have shown how the range of an isotropic pairwise additive potential determines the structure of atomic clusters. In particular, we have identified four principal structural regimes. For long-ranged potentials at sizes N=10-18 and N>45 the global minima are generally polytetrahedral and can be analyzed in terms of disclination lines. For the smaller clusters the disclinations form ordered arrangements and the structures are fragments of bulk Frank-Kasper phases. As the size increases it becomes more likely that the disclination network is a disordered tangle; these global minima have amorphous structures similar to those exhibited by liquid-like clusters. At intermediate ranges of the potential icosahedra are dominant. As the range decreases, first decahedral and then fcc structures become lowest in energy. These trends have been explained by considering the strain energies and the number of nearest neighbour contacts associated with each regime. The effect of decreasing the range of the potential is to destabilize the strained structures.