Hi Mark,
I tried the "Isomorphous difference map” action and specified a file for input 1 containing F1+, F1– at one wavelength, and the file input 2 containing F2+,F2– at another wavelength. I selected the appropriate Labels for the columns containing the anomalous data. I then specified in "Advanced Options” to *use anomalous differences instead of amplitudes*. Will this procedure use the following coefficients for the difference Fourier?
( F1(+) – F1(–) ) – ( F2(+) – F2(–) ), alpha(calc)
Can someone confirm if this is indeed what is calculated?
no, not quite.. Given two data sets, Fobs1 and Fobs2, and a phase source (eg., atomic model), it computes (Fobs1-scale*Fobs2, Phase) Fourier map. Both data sets are assumed to be collected from isomorphous crystals (same space groups, unit cells can deviate up to a small tolerance). Phenix treats Fobs(+) and Fobs(-) as individual data points, so in the map above they will participate as, for example (Fobs1(+)-scale*Fobs2(+), Phase) (Fobs1(-)-scale*Fobs2(-), Phase) Pavel