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\begin{document}

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\begin{gather*}
  E = D_0 [\exp^{-2 \alpha (r-r_0)} - 2\exp^{-\alpha (r-r_0)}] - s_6 \frac{C_6}{r^6} f_{damp}(r,R_r) \\
  f_{damp}(r,R_r) = \frac{1}{1 + \exp^{-d(r/R_r - 1)}}
\end{gather*}

\end{document}