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 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.