Hello, A portion of my structure have two conformations at an interface between two (NCS) protein chains -in addition to other alternates conformations elsewhere. In both chains, I defined alt_A as one conformation and alt_B as the second conformation, and also for the waters in this region. I would like to constrained the occupancy of these conformations. I though that the following selections would do the job: occupancies { constrained_group { selection = "(chain A or chain B) and (resseq 105 or resseq 110:112 or resseq 140:143) and altid A" After refinement, all alt_A selected residues do have the same occupancy, but not the same occupancies for alt_B and the sum for one residue (occu alt_A +occu alt_B) is not 1. Adding a second group with the same selection but "altid B", constrains also the alt_B occupancies but the sum is still not 1. How should I defined my group(s)? Is it possible to select several non continuous residues from one chain (that's for the waters) without repeating each time "or resseq" ? Best regards, Lionel