\begin{equation}
\label{eq:LJ}
(U_{\rm LJ})_{{\mu}i,{\nu}j} = 
U_{\rm LJ}(\epsilon_{{\mu}i,{\nu}j},a_{{\mu}i,{\nu}j},r_{{\mu}i,{\nu}j})=
4\epsilon_{{\mu}i,{\nu}j}
\left[\left(\frac{a_{{\mu}i,{\nu}j}}{r_{{\mu}i,{\nu}j}}\right)^{12}
-\left(\frac{a_{{\mu}i,{\nu}j}}{r_{{\mu}i,{\nu}j}}\right)^{6}\right]
\end{equation}
