Hey, my goal is to change the dihedrals of an already existing pdb template in order to find low-energy protein conformations. The issue I have here is that for some residues the dihedrals phi and psi cannot be changed. That's the error I get: Traceback (most recent call last): File "/home/nick/.local/UCSF-Chimera64-1.11.2/share/chimeraInit.py", line 683, in init chimera.openModels.open(a, prefixableType=1) File "/home/nick/.local/UCSF-Chimera64-1.11.2/share/chimera/__init__.py", line 1929, in open models = func(filename, *args, **kw) File "/home/nick/.local/UCSF-Chimera64-1.11.2/share/chimera/__init__.py", line 1299, in _openPython loadFunc(sandboxName, fileName, f) File "predictor.py", line 40, in <module> es.main_loop(); File "/home/nick/Python/pdb/AbstractOptimizer.py", line 97, in main_loop self.fs, self.evals, self.terminate = self.eval_pop(self.eval_func,self.pop,self.evals,self.eval_budget,self.extra_par) File "/home/nick/Python/pdb/eval_energy.py", line 20, in eval_energy allR[j].phi = pop[i,j]; File "/home/nick/.local/UCSF-Chimera64-1.11.2/share/chimera/phipsi.py", line 98, in setPhi _setAngle(bond, phi, getPhi(res, missingIsError=True), "phi", anchorSide) File "/home/nick/.local/UCSF-Chimera64-1.11.2/share/chimera/phipsi.py", line 147, in _setAngle br = BondRot(bond) ValueError: bond is part of a cycle Is there a way to determine beforehand which bonds are part of circle and hence which residues' dihedral information cannot be changed? Thank you in advanced for your time, Nikolaos Bismpikos