Dear phenix bb, I am trying to refine a ligand in the active site of my protein where the ligand occupancy is ~50%. The empty active site contains two chloride ions and the residual density from these ions is very prominent when the model is refined with the ligand alone. I would like to refine the model with both the ligand and chloride ions present and have been trying to do this with altLoc flags but so far with no luck. I'm assuming that since the Cl ions more-or-less directly overlay atoms from the ligand positional refinement keeps pushing them out of the density. I'm sure there is a simple way to get around this and I would be grateful for any suggestions. Best wishes, Steve Dr Stephen Carr Research Complex at Harwell (RCaH) Rutherford Appleton Laboratory Harwell Oxford Didcot Oxon OX11 0FA United Kingdom Email [email protected] tel 01235 567717 This email and any attachments may contain confidential, copyright and or privileged material, and are for the use of the intended addressee only. If you are not the intended addressee or an authorized recipient of the addressee, please notify us of receipt by returning the e-mail and do not use, copy, retain, distribute or disclose the information in or attached to this email. Any views or opinions presented are solely those of the author and do not necessarily represent those of the Research Complex at Harwell. There is no guarantee that this email or any attachments are free from viruses and we cannot accept liability for any damage which you may sustain as a result of software viruses which may be transmitted in or with the message. We use an electronic filing system. Please send electronic versions of documents, unless paper is specifically requested. This email may have a protective marking, for an explanation, please see: http://www.mrc.ac.uk/About/informationandstandards/documentmarking/index.htm.