7.4 fitting the energy levels
We minimise the \(\chi^2\) \[ \chi^2= \sum_i \frac{( \Delta E_2^{predicted} -\Delta E_2^{latt})^2}{\sigma^2} \]
\[\begin{gather} \chi^2/d.o.f.=0.721013 \\ P[0]=-0.15117\pm (0.0015) \\ P[1]=-3.11194\pm (0.13) \\ \end{gather}\] {\[\begin{gather} C=\begin{pmatrix} 1& 0.0011\\ 0.0011& 1\\ \end{pmatrix} \end{gather}\]}