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\begin{eqnarray*}
E_{LJ} & = & 4 \epsilon \left[ \left(\frac{\sigma}{r}\right)^{12} - 
                       \left(\frac{\sigma}{r}\right)^6 \right] + S_{LJ}(r)
                       \qquad r < r_c \\
E_C & = & \frac{C q_i q_j}{\epsilon  r} + S_C(r) \qquad r < r_c \\
S(r) & = & 0 \qquad r < r_1 \\
S(r) & = & A (r - r_1)^2 + B (r - r_1)^3 \qquad  r_1 < r < r_c
\end{eqnarray*}                           

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