in which D e is a "dissociation energy" representing the well depth, α is in units of inverse length and controls how steep the function is and r eqm represents the equilibrium distance between two atoms. Unless otherwise specified, the equilibrium bond length parameter takes the value r eqm = 50.0 nm, the steepness parameter takes the value α = 0.150 nm -1 and the dissociation energy takes the value D e = 16.5 × 10 -21 J. This equation has the properties that lim r→∞ U(r) = 0 and lim r→∞ -dU dr = 0, meaning that the forces and energies in the system are unaffected if the breaking cutoff is set sufficiently large.