Fix typos in caption for LR electrostatics, improve clarity

Author: davidlmobley

paper/basic_training.tex

@@ -1058,7 +1058,7 @@ \subsubsection{ Ewald Summation}
 \centering
 \includegraphics[width=\linewidth]{ewald.pdf}
 
-    \caption{\label{fig:screening}Screening charge distribution. (top) Original charge distribution. (bottom)Point charges can be split into Direct space(blue) and Reciprocal space charges(red). Direct space charge consists of the original charges and gaussian-distributed screening charge. Reciprocal space charge is only the Gaussian-distributed charge. }
+    \caption{\label{fig:screening}Screening charge distribution. (Top) The original charge distribution. (Bottom) Point charges can be split into Direct space (blue) and Reciprocal space charges (red). The direct space charge consists of the original charges and Gaussian-distributed screening charges of opposite sign. The reciprocal space charge is only the Gaussian-distributed charge of the original sign. Together these sum to the original charge distribution, but computation of the electrostatic potential due to each component becomes much easier.}
 \label{charges_ewald}
 \end{figure}