Exp-6 potential

The exp-6 potential is given by (Eq. 1 in ^[1]):

\Phi _{12}(r)={\frac {\epsilon }{1-6/\alpha }}\left[\left({\frac {6}{\alpha }}\right)\exp \left[\alpha \left(1-{\frac {r}{\sigma }}\right)\right]-\left({\frac {\sigma }{r}}\right)^{6}\right]

where

$r:=|\mathbf {r} _{1}-\mathbf {r} _{2}|$
$\Phi _{12}(r)$ is the intermolecular pair potential between two particles or sites
$\sigma$ is the value of $r$ at which $\Phi _{12}(r)=0$
$\epsilon$ is the well depth (energy)
$\alpha$ is the "steepness" of the repulsive energy