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

The growth of self-interstitial clusters in crystalline Si is investigated by semi-empirical 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 all evolutionary path from compact (n < 5) to elongated (n greater than or equal to 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.