Evolution of energetics and bonding of compact self-interstitial clusters in silicon

The growth of self-interstitial clusters in crystalline Si is investigated by semiempirical tight-binding molecular dynamics. The equilibrium configuration of each n-interstitial cluster (n = 2-11) has been obtained by adding one more dumbbell defect to the previously relaxed (n - 1) SI cluster in the series. We find an evolutionary path from compact (n < 5) to elongated (n >= 5) clusters. We relate the shape evolution of clusters to the changes in their atomic coordination and bonding properties, using first principles structure calculations and a topological analysis of their associated electron densities.