fixed figure 7 reference

Author: samarjeet

paper/basic_training.pdf

@@ -1058,7 +1058,7 @@ \subsubsection{ Ewald Summation}
 \label{charges_ewald}
 \end{figure}
 
-Unlike the original, full potential, the direct space screened interaction (Figure~\ref{fig:screening}, top) decays rapidly (Figure~\ref{charges_ewald}).
+Unlike the original, full potential, the direct space screened interaction (Figure~\ref{fig:screening}, top) decays rapidly (Figure~\ref{decay}).
 In fact, it decays even faster than van der Waals interactions ($1/r^{6}$) and hence relative short cutoffs, comparable to those used for van der Waals interactions, can be used for handling direct-space Coulomb interactions.