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New Vector Parametrization of Accessible Arcs

Definitions: xi : Cartesian coordinates of atom i; xik = xk-xi ; dik = |xik| : interatomic distance vector and its length; µik = xik/dik : unit vector along xik ; gik = [(dik)2 + ri2 + rk2]/[2dik]: distance to the center of the ik-th intersection circle; nikj = [µik×Pikj]/aik ; mikl = [µik×Qikl]/aik : tangential unit vectors; Sikjl = sign[µik· (nikj×mikl)] : orientation of the tangential vectors.