STRUCTURAL CONSEQUENCES OF THE RANGE OF THE INTERATOMIC POTENTIAL - AMENAGERIE OF CLUSTERS

We have attempted to find the global minima of clusters containing bet ween 20 and 80 atoms bound by the Morse potential, as a function of th e range of the interatomic force. The effect of decreasing the range i s to destabilize strained structures, and hence the global minimum cha nges from icosahedral to decahedral to face-centred-cubic as the range is decreased. For N > 45, the global minima associated with a long-ra nged potential have polytetrahedral structures involving defects calle d disclination lines. For the larger clusters, the network of disclina tion lines is disordered and the global minimum has an amorphous struc ture resembling a liquid. The size evolution of polytetrahedral packin gs enables us to study the development of bulk liquid structure in fin ite systems. As many experiments on the structure of clusters only pro vide indirect information, these results will be very useful in aiding the interpretation of experiment. They also provide candidate structu res for theoretical studies using more specific and computationally ex pensive descriptions of the interatomic interactions. Furthermore, Mor se clusters provide a rigorous testing ground for global optimization methods.