Dear all, I am a 2nd year PhD student who just started working on crystallography. I am now trying to solve a structure by SAD. The data quality is poor, with a resolution of 4.9 A and anomalous signal up to 5.5-6 A. I am using hkl2map to locate the heavy atoms, and I have a few questions concerning the CC and PATFOM in shelxd.
1) I do have several "solutions" whose CC seems to be well separated from the majority (highest CCall/CCweak=35.8/16.5), however, their PATFOM are rather low. On the other hand, I got a well separated PATFOM, but its CCall is only 25.4. (see attached) How could this happen? I tried to search online for how shelxd calculates CC and PATFOM but didn't get a clear answer. 2) In the native dataset of crystals from similar conditions, pseudo-translation is detected (34.36% off-origin peak compared to the origin peak in the native Patterson map). Would this pseudo-translation peak bias the Patterson seeding in shelxd? I switched off the Patterson seeding and got worse CCall but better CCweak (30.4/19.3). Is this an intrinsic trend in shelxd or can it tell something about the data? Does this pseudo-translation peak have something to do with the extremely high PATFOM mentioned in 1)? Your answers will be greatly appreciated. Sincerely, Chen
<<attachment: ccall-ccweak.png>>
<<attachment: ccall-patfom.png>>
