+\r
+\subsection{C$_{\text{i}}$ next to C$_{\text{s}}$}\r
+\r
+The first row of Table~\ref{table:dc_c-sv} lists the binding energies of C$_{\text{s}}$ next to the C$_{\text{i}}$ \hkl[0 0 -1] DB.\r
+For C$_{\text{s}}$ located at position 1 and 3 the configurations a and A correspond to the naive relaxation of the structure by substituting a Si atom with C in the initial C$_{\text{i}}$ \hkl[0 0 -1] DB structure at positions 1 and 3 respectively.\r
+However, small displacements of the involved atoms near the defect result in different stable structures labeled b and B respectively.\r
+\r
+% A B\r
+Configuration A consists of a C$_{\text{i}}$ \hkl[0 0 -1] DB with threefold coordinated Si and C DB atoms slightly disturbed by the C$_{\text{s}}$ at position 3, facing the Si DB atom as a next neighbor.\r
+By breaking a Si-Si in favor of a Si-C bond configuration B is obtained, which shows a twofold coordinated Si atom located inbetween two substitutional C atoms residing on regular Si lattice sites.\r
+This configuration has been identified and described by spectroscopic experimental techniques\cite{song90_2} as well as theoretical studies\cite{leary97,capaz98}.\r
+Configuration B is found to constitute the energetically more favorable configuration.\r
+However, the gain in energy due to the significantly lower energy of a Si-C compared to a Si-Si bond turns out to be smaller than expected due to a large compensation by introduced strain as a result of the Si interstitial structure.\r
+Present results show a difference in energy of states A and B, which exactly matches the experimental value of \unit[0.02]{eV}\cite{song90_2} reinforcing qualitatively correct results of previous theoretical studies on these structures.\r
+% mattoni: A favored by 0.4 eV - NO, it is indeed B (reinforce Song and Capaz)!\r
+%\r
+% AB transition\r
+%Figure~\ref{fig:AB} displays the two configurations and migration barrier for the transition among the two states.\r
+\r
+% a b\r
+Configuration a is similar to configuration A except that the C$_{\text{s}}$ at position 1 is facing the C DB atom as a next neighbor resulting in the formation of a strong C-C bond and a much more noticeable perturbation of the DB structure.\r
+Nevertheless, the C and Si DB atoms remain threefold coordinated.\r
+Although the C-C bond exhibiting a distance of \unit[0.15]{nm} close to the distance expected in diamond or graphite should lead to a huge gain in energy, a repulsive interaction with a binding energy of \unit[0.26]{eV} is observed due to compressive strain of the Si DB atom and its top neighbors (\unit[0.230]{nm}/\unit[0.236]{nm}) along with additional tensile strain of the C$_{\text{s}}$ and its three neighboring Si atoms (\unit[0.198-0.209]{nm}/\unit[0.189]{nm}).\r
+\r
+...\r
+\r
+Liu et~al.\cite{liu02} propose a similar structure \unit[0.2]{eV} lower than configuration B, thus, constituting the ground state configuration.\r
+The structure labeld b indeed is the ground state configuration, in which the two C atoms form a \hkl[1 0 0] DB sharing the C$_{\text{s}}$ lattice site and the initial Si DB atom occupying the lattice site shared by the initial C$_{\text{i}}$ DB.\r
+\r
+Spin polarization for C-C Int resulting spin up electrons located as in the case of the Si 100 int.\r
+% mattoni: A favored by 0.2 eV - NO! (again, missing spin polarization?)\r