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+\documentclass[12pt]{article}
+
+\begin{document}
+
+\begin{eqnarray*}
+ F & = & F_{\mathrm{LJ}}(r) - F_{\mathrm{LJ}}(r_{\mathrm{c}}) \qquad r < r_{\mathrm{c}} \\
+ E & = & E_{\mathrm{LJ}}(r) - E_{\mathrm{LJ}}(r_{\mathrm{c}}) + (r - r_{\mathrm{c}}) F_{\mathrm{LJ}}(r_{\mathrm{c}}) \qquad r < r_{\mathrm{c}} \\
+ \mathrm{with} \qquad E_{\mathrm{LJ}}(r) & = & 4 \epsilon \left[ \left(\frac{\sigma}{r}\right)^{12} - \left(\frac{\sigma}{r}\right)^6 \right] \qquad \mathrm{and} \qquad F_{\mathrm{LJ}}(r) = - E^\prime_{\mathrm{LJ}}(r)
+\end{eqnarray*}                           
+
+\end{document}