Dear all, thanks to the phenix team which helped me a lot to resolve all issues regarding the correct link definitions. I have summarised a few things which one might consider if nonstandard links are necessary. Try phenix ready set to get your links out of the pdb. Do not forget to change the possible LINKR to LINK! Inspect the links and decide if they are useful! Peptide links are automatically incorporated if residues are close (inspect geo file) Non standard peptide links could be created using using an now available alpha release script: elbow.ligand_linking model.pdb Inspect the generated cif file and correct angles and incorporate dihedrals and so on if necessary. Sugar links which exists in the mon_lib.cif should be incorporated using the apply_cif link option like refinement.pdb_interpretation.apply_cif_link { data_link = ALPHA1-4 residue_selection_1 = chain B and resname GLC and resseq 1 residue_selection_2 = chain B and resname GLC and resseq 2 } According to the link definition the C1 oxygen of the following sugar with the higher number must be removed. The automatic incorporation of sugar links will be probably soon available in phenix. Nigel is already working on this. If one want use hydrogens in the refinement, they have to be added previously with ready_set and afterwards the OH4 sugar hydrogen has to be removed before the refinement. For links with symmetry related atoms the symmetry operator must be included in a custom bond definition efinement.geometry_restraints.edits { bond { action = *add delete change atom_selection_1 = chain A and resname HEM and resid 154 and name FE atom_selection_2 = chain A and resname MTO and resid 155 and name O symmetry_operation = -x,y,-z distance_ideal = 2.2 sigma = 0.01 } } The operator can be obtained using iotbx.show_distances your.pdb > all_distances Search for keyword "sym" or from Coot clicking on the symm option. Coot print out the operator and the translation term separately. Both has to be merged in the final operator used in phenix! Christian