The formation energies are $2.7\, eV$ and $1.8\, eV$ respectively.
Again the hexagonal one is found to be unstable.
The interstitial atom moves to the more favorable <100> dumbbell position which has a formation energy of $0.5\, eV$.
The interstitial configuration is shown in Fig. 2.
There is experimental evidence \cite{watkins76} of the existence of this configuration.
It is frequently generated and has the lowest formation energy of all the defects observed in all the simulation runs in which carbon is inserted at random positions.
The formation energies are $2.7\, eV$ and $1.8\, eV$ respectively.
Again the hexagonal one is found to be unstable.
The interstitial atom moves to the more favorable <100> dumbbell position which has a formation energy of $0.5\, eV$.
The interstitial configuration is shown in Fig. 2.
There is experimental evidence \cite{watkins76} of the existence of this configuration.
It is frequently generated and has the lowest formation energy of all the defects observed in all the simulation runs in which carbon is inserted at random positions.