1. J Lebowitz and O Penrose,Phys. Today, February 1973, p. 23
2. See, e.g.The physics and chemistry of small clusters, edited by P Jena, B K Rao and S N Khanna, (New York, Plenum, 1987)
3. Physics and Chemistry of finite systems: From clusters to crystals, edited by P Jena, S N Khanna and B K Rao, (Kluwer Dordrecht, 1992)
4. Clusters of atoms and molecules, edited by H. Haberland (Springer-Verlag, 1994)
5. R S Berry, inClusters of atoms and molecules, edited by H Haberland (Springer-Verlag, 1994)