+As mentioned earlier the procedure to obtain the migration barriers differs from the usually applied procedure in two ways.
+Firstly constraints to move along the displacement direction are applied on all atoms instead of solely constraining the diffusing atom.
+Secondly the constrainted directions are not kept constant to the initial displacement direction.
+Instead they are updated for every displacement step.
+These modifications to the usual procedure are applied to avoid abrupt changes in structure and free energy on the one hand and to make sure the expected final configuration is reached on the other hand.
+Due to applying updated constraints on all atoms the obtained migration barriers and pathes might be overestimated and misguided.
+To reinforce the applicability of the employed technique the obtained activation energies and migration pathes for the \hkl<0 0 -1> to \hkl<0 -1 0> transition are compared to two further migration calculations, which do not update the constrainted direction and which only apply updated constraints on three selected atoms, that is the diffusing C atom and the Si dumbbell pair in the initial and final configuration.
+Results are presented in figure \ref{fig:defects:00-1_0-10_cmp}.
+\begin{figure}[th!]
+\begin{center}
+\includegraphics[width=13cm]{vasp_mig/00-1_0-10_nosym_sp_cmp.ps}
+\end{center}
+\caption[Comparison of three different techniques for obtaining migration barriers and pathways applied to the \hkl<0 0 -1> to \hkl<0 -1 0> C-Si dumbbell transition.]{Comparison of three different techniques for obtaining migration barriers and pathways applied to the \hkl<0 0 -1> to \hkl<0 -1 0> C-Si dumbbell transition.}
+\label{fig:defects:00-1_0-10_cmp}
+\end{figure}
+The method without updating the constraints but still applying them to all atoms shows a delayed crossing of the saddle point.
+This is understandable since the update results in a more aggressive advance towards the final configuration.
+In any case the barrier obtained is slightly higher, which means that it is not the energetically most favorable pathway.
+The method in which the constraints are only applied to the diffusing C atom and two Si atoms, ... {\color{red}in progress} ...
+
+\subsection{Migration barriers obtained by classical potential calculations}
+
+The same method for obtaining migration barriers and the same suggested pathways are applied to calculations employing the classical Erhard/Albe potential.
+
+\begin{figure}[th!]
+\begin{center}
+\includegraphics[width=13cm]{bc_00-1.ps}
+\end{center}
+\caption{Migration barrier of the bond-centered to \hkl<0 0 -1> dumbbell transition using the classical Erhard/Albe potential.}
+\label{fig:defects:cp_bc_00-1_mig}
+\end{figure}
+Figure \ref{fig:defects:cp_bc_00-1_mig} shows the migration barrier of the bond-centered to \hkl<0 0 -1> dumbbell transition.
+Since the bond-centered configuration is unstable within this potential the low kinetic energy state is used as a starting configuration.
+This would relax towards the \hkl<1 1 0> C-Si interstitial.
+
+\begin{figure}[th!]
+\begin{center}
+\includegraphics[width=13cm]{00-1_0-10.ps}
+\end{center}
+\caption{Migration barrier of the \hkl<0 0 -1> \hkl<0 -1 0> C-Si dumbbell transition using the classical Erhard/Albe potential.}
+\label{fig:defects:cp_00-1_0-10_mig}
+\end{figure}
+Figure \ref{fig:defects:cp_00-1_0-10_mig} shows the migration barrier of the \hkl<0 0 -1> to \hkl<0 -1 0> C-Si dumbbell transition.
+After the first maximum the system relaxes to a configuration similar to the \hkl<1 1 0> C-Si dumbbell configuration.
+
+\begin{figure}[th!]
+\begin{center}
+\includegraphics[width=13cm]{00-1_ip0-10.ps}
+\end{center}
+\caption{Migration barrier of the \hkl<0 0 -1> to \hkl<0 -1 0> C-Si dumbbell transition in place using the classical Erhard/Albe potential.}
+\label{fig:defects:cp_00-1_ip0-10_mig}
+\end{figure}
+Figure \ref{fig:defects:cp_00-1_ip0-10_mig} shows the migration barrier of the \hkl<0 0 -1> to \hkl<0 -1 0> C-Si dumbbell transition in place.
+
+\section{Combination of point defects}