Lennard-Jones (LJ) parameterization for Xe. The LJ parameters epsilon and sigma are due to Bernardes (1958). The cutoff radius is set so that phi(rcut)=tol*|phi(rmin)|, where phi(r) is the LJ potential, 'rcut' is the cutoff radius, 'rmin' is the radius at which phi(r) is a minimum, and 'tol' is a small number. Here 'tol' is taken to be 1.e-3 for a "medium-precision". See the parameter file (.params) for more details.