convert wall fixes to embedded math

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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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$$ 

E = \epsilon \left[ \frac{2  \sigma_{LJ}^{12} \left(7 r^5+14 r^3 \sigma_{n}^2+3 r \sigma_{n}^4\right) }{945 \left(r^2-\sigma_{n}^2\right)^7} -\frac{ \sigma_{LJ}^6 \left(2 r \sigma_{n}^3+\sigma_{n}^2 \left(r^2-\sigma_{n}^2\right)\log{ \left[\frac{r-\sigma_{n}}{r+\sigma_{n}}\right]}\right) }{12 \sigma_{n}^5 \left(r^2-\sigma_{n}^2\right)} \right]\qquad \sigma_n < r < r_c

$$

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