First-Principles Calculations for Structures and Melting Temperature of Si₆ Clusters

We investigate the structures and the melting temperature of the Si₆ cluster by using the first-principles pseudopotential method in real space and Langevin molecular dynamics. It is shown that the ground structure of the Si₆ cluster is a square bipyramid, and the corresponding melting temperature is about 1923K. In the heating procedure, the structures of the Si₆ cluster change from high symmetry structures containing 5--8 bonds, via prolate structures containing 3--4 bonds, to oblate structures containing 1--2 bonds.