James is absolutely right = the wonder of crystallography is that the difference map can theoretically pinpoint errors and suggest what is missing in your model..
But also check your data - modern synchrotrons often measure some reflections to a high resolution limit, but the noise can get greater than the signal at the resolution limit.. Is the Wilson plot straight to the resolution limit? Is the second moment Of intensities (or the 4th moment of amplitudes) ~ 2? The data processing reports tell you these things. Eleanor On 15 September 2017 at 17:25, James Holton <jmhol...@slac.stanford.edu> wrote: > You know, I've been pondering that question for most of my adult life. > Why can't we push macromolecular R factors down to the level of > experimental error like our "small molecule" colleagues do routinely? I > have a few ideas, and others do too. In fact, there will be session on > this topic at the next ACA meeting. > > But right at this moment the best advice I can give you is to load up your > model and map in coot and use the Validate : Difference Map Peaks option. > The highest and lowest points in your FoFc map are the least likely of all > difference features to be due to noise. Look at them, and try to do > something about them. When you run out of ideas, you're done. Then you > look at your statistics. If the R factors are "too high" and the geometry > is way too good, then you need to increase the x-ray weight in refinement. > Once you've changed something in the refinement options, let it run for a > while so the programs can do their job. When things stop moving it is time > to look at maps again. The myriad of options in refinement and automatic > building features are all things that can save you time in this process, > but at the end of the day, it is the difference map that tells you what to > do next. > > -James Holton > MAD Scientist > > > On 9/15/2017 4:32 AM, rohit kumar wrote: > >> why R/Rfree not going down from 21/25? >> >
