A well-known deficiency of the Buckingham potential appears at very close ranges. As r 0Ii,lJj tends to zero, the exponential term converges to the value of A Ii,Jj while the r -6 0Ii,lJj term diverges asymptotically and dominates the former term. This leads to an unphysical attraction at very short ranges. In practice, this issue can be avoided as long as there is a sufficiently large energy barrier arising from the repulsive interaction at short-to-medium ranges. The size and location of this energy barrier is a function of parameters A Ii,Jj , B Ii,Jj , and C Ii,Jj and so it is important that suitable values are chosen to effectively 'insulate' against the unphysical parts of the Buckingham potential. However, during the parameter estimation process, if the values of several parameters related to the same pair potential are allowed to vary simultaneously, this can be challenging.