Epsilon parameter (dispersion energy) of Lennard-Jones interaction for this species.
In case two particles have a different epsilon, the combination rule will be computed
ϵ12=ϵ1+ϵ2.
Sigma parameter (particle size) of Lennard-Jones interaction for this species.
In case two particles have a different sigma, the combination rule will be computed
$\sigma_{12} = (\sigma_1 + \sigma_2) / 2.