Thermal properties of medium-sized Ge clusters

The thermal behavior of germanium clusters is studied by using tight-binding molecular dynamics. The lowest energy structures of Gen clusters up to 21 atoms are optimized with a genetic algorithm. Some high symmetric layered structures are found in medium-sized clusters and large clusters can be constructed from small cluster subunits. We discuss the melting temperature as a function of the cluster size. Even-odd alternation is found in the size range n=11–17. The Gen clusters with n=7, 12 and 19 have particularly high melting points, which correspond to the relatively high stabilities of their ground state structures. We find that the large clusters can be dissociated into small clusters upon heating and an interesting two-stage melting behavior is revealed in the case of Ge21.