Dear Paul, That implies that phenix refine (like SHELXL, but unlike REFMAC) can refine against data for which I+ and I- (or F+ and F-) have not been merged. An attempt to refine f" against Friedel merged data would be very poorly determined. Am I right in guessing that phenix refine can only do this when then structure factors are calculated by the classical summation and not by FFT?
Given relatively high resolution MAD data, it is at least theoretically possible using SHELXL (and presumably also phenix refine) to refine against I+ and I- for all wavelengths at once, this should give much better occupancies for the selenium atoms (in the case of SHELXL it would be necessary to use HKLF 2 input format so that a wavelength is specified for each reflection, refine batch scale factors, use the LAUE instruction so that the program can work out f' and f" for each reflection, and - at least when each site is assumed to be Se or S in different ratios - use 'free variables' for the Se occupancies). If anyone is MAD enough to try this, I would also recommend scaling against a reference dataset (e.g. high energy remote) rather than scaling the data for different wavelengths separately. There is a suitable option in SCALA and SADABS and possibly in other scaling programs as well. Best wishes, George Prof. George M. Sheldrick FRS Dept. Structural Chemistry, University of Goettingen, Tammannstr. 4, D37077 Goettingen, Germany Tel. +49-551-39-3021 or -3068 Fax. +49-551-39-2582 On Sat, 11 Aug 2007, Paul Adams wrote: > Hi Ethan, > > if you want you can specify and refine both f' and f'' for any user selected > atoms in phenix.refine: > > http://www.phenix-online.org/download/ > > > Cheers, > Paul > > On Aug 11, 2007, at 9:48 PM, Ethan A Merritt wrote: > > > On Saturday 11 August 2007 21:41, Miller, Mitchell D. wrote: > > > Hi Ethan, > > > > > > > I have been wanting a way to instruct refmac to accept a user- > > > > defined > > > > f' term since about forever. > > > > > > According to Garib's latest release notes, a command was > > > added to refmac 5.3.0015 and later to allow f' to be specified. > > > I have not tried it myself yet.. see > > > http://www.ysbl.york.ac.uk/~garib/refmac/data/refmac_news.html > > > "Anomolous form factors > > > > > > anom formfactor [Name] [f'] [f''] > > > > > > It will modify form factor of the given atom and use f' part only" > > > > <goes off to install a newer refmac version/> > > > > Thanks, > > > > Ethan > -- > Paul Adams > Senior Scientist, Physical Biosciences Division, Lawrence Berkeley Laboratory > Adjunct Professor, Department of Bioengineering, U.C. Berkeley > Head, Berkeley Center for Structural Biology > Deputy Principal Investigator, Berkeley Structural Genomics Center > > Building 64, Room 248 > Tel: 510-486-4225, Fax: 510-486-5909 > http://cci.lbl.gov/paul > > Lawrence Berkeley Laboratory > 1 Cyclotron Road > BLDG 64R0121 > Berkeley, CA 94720, USA. > -- > >