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\begin{document}
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\Large
\begin{eqnarray*}
  E & = & \frac{1}{2} \sum_i \sum_{j \neq i} V_{ij} \\[15pt]
  V_{ij} & = & {\rm Tap}(r_{ij})\frac{\kappa q_i q_j}{\sqrt[3]{r_{ij}^3+(1/\lambda_{ij})^3}}\\[15pt]
  {\rm Tap}(r_{ij}) & = & 20\left ( \frac{r_{ij}}{R_{cut}} \right )^7 -
                          70\left ( \frac{r_{ij}}{R_{cut}} \right )^6 +
                          84\left ( \frac{r_{ij}}{R_{cut}} \right )^5 -
                          35\left ( \frac{r_{ij}}{R_{cut}} \right )^4 + 1
\end{eqnarray*}
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\end{document}
