+Substitutional carbon in silicon is found to be the lowest configuration in energy for all potential models.
+
+
+
+Except for Tersoff's tedrahedral configuration results the \hkl<1 0 0> dumbbell is the energetically most favorable interstital configuration.
+The low energy of formation for the tetrahedral interstitial in the case of the Tersoff potential is believed to be an artifact of the short cutoff (see ref. 13 in \cite{tersoff90}) and the real formation energy is supposed to be located between 3 and 10 eV.
+The formation energy for substitutional carbon is about 3 eV lower than the \hkl<1 0 0> dumbbell for both classical potentials.
+
+The highest energy is observed for the hexagonal interstitial configuration using classical potentials.
+Quantum-mechanical calculations reveal this configuration to be unstable, which is also reproduced by the Erhard/Albe potential.
+In both cases a relaxation towards the \hkl<1 0 0> dumbbell configuration is observed.
+
+\subsection[\hkl<1 0 0> dumbbell interstitial configuration]{\boldmath\hkl<1 0 0> dumbbell interstitial configuration}