commit JT 020818

- adding files for doc and reorg.

doc/src/Eqs/pair_spin_exchange_forces.tex

@@ -0,0 +1,14 @@
+\documentclass[preview]{standalone}
+\usepackage{varwidth}
+\usepackage[utf8x]{inputenc}
+\usepackage{amsmath,amssymb,amsthm,bm}
+\begin{document}
+\begin{varwidth}{50in}
+  \begin{equation}
+    \vec{F}^{i} = \sum_{j}^{Neighbor} \frac{\partial {J} \left(r_{ij} \right)}{
+    \partial r_{ij}} \left( \vec{s}_{i}\cdot \vec{s}_{j} \right) \vec{r}_{ij}  
+    ~~{\rm and}~~ \vec{\omega}^{i} = \frac{1}{\hbar} \sum_{j}^{Neighbor} {J} 
+    \left(r_{ij} \right)\,\vec{s}_{j} \nonumber
+  \end{equation}
+\end{varwidth}
+\end{document}