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Hi Mike and other interested colleagues, I agree - it is best to select the observed data with the same indices for the new Rfree set as in the previous isomorphous crystal(s), selecting new ones for higher resolution shells (which can be conveniently done in XDS during conversion to other formats with XDSCONV). However, in my experience, even if a completely new random Rfree set is chosen, it will "de-couple" from its initial bias after many cycles of refinement, even without any random perturbations of the model or simulated annealing. You can see how many cycles are needed by monitoring the difference between R and Rfree, which should converge at a maximum value if you don't change the model or the refinement parameters in between. Best regards, Dirk. Am 24.09.2009 um 10:36 schrieb Eleanor Dodson: > Mike England wrote: >> Hi all, >> >> I will appreciate your comments on the following case: >> >> I have two datasets from the same or identical crystals. Initially, I >> refine a structure against the first data set and later on switch to >> another dataset for further refinements. >> Do you think, my Rfree will be biased as Rfree reflections in second >> dataset may be in fact Rwork reflections in previous datasets ? >> >> Thanks in advance, >> >> Mike >> >> >> > Yes [- it will be biased, but why arent preserving the same Rfree > set from crystal 1 into the crystal 2 assignmenmt, only selecting > new free reflections at the higher resolution data from crystal 2 > > If you are running scala or import scaled data t make an mtz file > there is an option: > Click Ensure Free R and Copy freeR from another mtz > > Eleanor ******************************************************* Dirk Kostrewa Gene Center, A 5.07 Ludwig-Maximilians-University Feodor-Lynen-Str. 25 81377 Munich Germany Phone: +49-89-2180-76845 Fax: +49-89-2180-76999 E-mail: [log in to unmask] WWW: www.genzentrum.lmu.de *******************************************************