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Besides possibilities pointed, I would ask if your are using undue NCS restraints, id est, between "rotamers" which are genuinely "different". Anyway, at 1.8 A resolution, one should check the adequateness of using NCS restraints. J > Hi, > > I'm working with a 1.8 A structure with Coot and Refmac, and there > are many sidechain rotamers that show very clear difference density > peaks for setting their correct positions. However, Refmac > continuously moves the rotamers back into negative density peaks. > It's really quite silly because often there is an obvious positive > density peak near to a negative density peak. > > I have tried using automatic geometry weighting and manually setting > the weighting term to a very tight 0.025, but each has no effect. I > have also tried increasing the torsion angle restraint term to 2.0 > but this also has no effect. > > Does anyone have any suggestions? Is there any way to "fix" atom > positions for Refmac? > > Thanks in advance, > > ~ > Peter J Stogios, Ph.D. > Postdoctoral Research Fellow > e: [log in to unmask] > p: 416-978-4033 > w: http://www.uhnres.utoronto.ca/centres/proteomics/ > > Structural Proteomics in Toronto Research Group, University Health Network > C.H. Best Institute > 112 College Street, Room 70 > Toronto, Ontario, Canada M5G 1L6 >