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\begin{eqnarray}
E &=& \epsilon \left[ \frac{\sigma^{6}}{7560} 
  \left(\frac{6R-D}{D^{7}} + \frac{D+8R}{(D+2R)^{7}} \right) - 
  \frac{}{} \right. \nonumber \\
  &&\qquad \left. \frac{1}{6} \left(\frac{2R(D+R) + D(D+2R)
    \left[ \ln D - \ln (D+2R) \right]}{D(D+2R)} \right) \right] 
\qquad r < r_c \nonumber
\end{eqnarray}

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