More restrictive condition for creating crossover dihedral potentials

mrdna/segmentmodel.py

@@ -2698,11 +2698,12 @@ class SegmentModel(ArbdModel):
 
                 # if n2.idx == 0:
                 #     print( n1.idx,n2.idx,n3.idx,n4.idx,k,t0,sep )
-                # if sep == 0 and n1 is not n4:
                 if sep == 0:
                     # pot = self.get_angle_potential(k,t0)
                     # self.add_angle( n1,n2,n4, pot )
                     pass
+                elif len(set((n1,n2,n3,n4))) != 4:
+                    print("WARNING: skipping crossover dihedral angle potential because beads are too close")
                 else:
                     pot = self.get_dihedral_potential(k,t0)
                     self.add_dihedral( n1,n2,n3,n4, pot )