Dear All, I am trying to select different regions of the same protein to be included in the same NCS group before refinement. This correspond to the core of a protein. Additionally, I would define other NCS groups for external domains. I have 4 protein/RNA complexes in the asu, P1. Here are the residue ranges for the NCS group corresponding to the core of the protein (invariant): Chain A and resseq: 1:156, 188-227, 413:568, 629:794 this should be the reference group, to match the same region in the other 3 monomers (C, E. G). Other NCS groups will include the RNA, as well as other external domains: Chain B and resseq: 1: 87 This is the RNA molecule, that should match the other 3 monomers (D, F, H) Chain A resseq: 157:187 this is a external domain, to match the other protein monomer (C, E, G) and so on.... for other external domain I have seen that there is the possibility to use user-defined NCS groups, by using: * ncs_groups.params * or modifying the GUI by editing the atom selection For the external domains I think is easy as the syntax is only one line, however for the core of the protein I do not manage to select properly the different residue ranges. Could anybody please help on that? what would be the easiest way to do that? Can I for example creat a ncs_groups.params file and add it to phenix.refine in the GUI? Thanks in advance, Andres