Finally, we compare FB-ENM and IDPP from a theoretical perspective. Section 2.1 listed four unfavorable factors of IDPP: (i) constraints on all atom pairs, (ii) forcing linear interpolation of interatomic distances, (iii) decrease of pair potential v(r; d) at r > 2d, and (iv) divergence of v(r; d) at r = 0. FB-ENM addresses these problems as follows.