Melting transition of small molecular clusters

The melting behaviour for finite size clusters is calculated in the framework of positional disorder theory. It is shown that the 'melting anomalies' observed in a variety of absorbate systems, such as H2O in porous Al2O and N2 or Ar on TiO2, are consistent with the melting characteristics of small clusters. In particular, the specific heat of small clusters exhibits a broadened peak centred at temperatures below the bulk melting point Tm. As the cluster size increases, the peak tends to sharpen and shift closer to Tm. Furthermore, the theory predicts a characteristic size for the onset of bulk first-order melting transition behaviour.