Pathway connecting the four-interstitial ground state and chain in silicon

Dimer searches, minima hopping and nudged elastic band (NEB) calculations try to identify the lowest pathway connecting the two important silicon four-interstitial structures: $I_4$-chain and ground state. First, 400 tight-binding dimer searches reveal several local minima. However, the minima have high DFT formation energies and no pathway connecting chain and ground state is found. Second, we fit a classical modified embedded atom method potential to a database of interstitial clusters. Minima hopping using this potential finds several structures with DFT energies between chain and ground state but no pathway connecting them. Finally, we construct a pathway between chain and ground state with small displacements. The NEB energy barrier with DFT from chain to ground state is 0.6~eV. This indicates that during annealings the $I_4$-chain decays into the nearly immobile ground state, implying that chain structures predominate only for longer chains.