Hello, PhenixBB. I am doing joint x-ray/neutron refinement of a hydrogenated protein crystal soaked in D2O buffers, and I've run into a problem with refinement. I hope you can help. I used phenix.ready_set to add deuterium atoms to the exchangeable hydrogen positions. I ran a perl script to set the initial occupancies of those to 0.5 H and 0.5 D (they had been output as 1.0). When I ran phenix.refine with riding hydrogen positions or with individual hydrogen positions, the H and D atoms refined to different positions. How can I constrain the H and D positions to be identical? Regards, Anna Gardberg -- Anna Gardberg Research Associate, Postdoctoral Center for Structural Molecular Biology Oak Ridge National Laboratory Bldg. 4500S, M/S 6142 Oak Ridge TN 37831-6142 phone: 865-576-2173