The Lennard-Jones potential in its various forms is described in a Wikipedia article. The truncation of the potential at large distances by a simple chop and lift operation is described, but there is no mention of splines to avoid discontinuous first derivatives, or of any special treatment at small distances. The canonical form of the potential is 4ε*[(σ/r)¹² - (σ/r)⁶]; an alternate form is D*[(R/r)¹² - 2*(R/r)⁶)]. The first one uses the distance at which the potential is zero (σ), the second uses the distance at which the potential is minimal (R). ε and D are the well depth in both cases.