As you observe, radiation damage is local, but the effect is - to different extent - on all Fs i.e. global (all atoms and their damage contribute to each hkl).
So one would need additional local parameters (reducing N/P) if you want to address it as such, your use of occupancy is an example (even if you have a reflection-specific decay, somehow a realistic underlying atomic model would be desirable, and just changing occ might not be ideal)..So is the question then 'Could a reflection-specific time dependent decay factor translate into any useful atom-specific model parameter? BR From: CCP4 bulletin board [mailto:[email protected]] On Behalf Of Jacob Keller Sent: Monday, March 19, 2012 7:46 AM To: [email protected] Subject: [ccp4bb] Refining Against Reflections? Dear Crystallographers, it occurred to me that most datasets, at least certainly since the advent of synchrotrons, have probably some degree of radiation damage, if not some huge degree thereof. Therefore, I was thinking an exposure-dependent parameter might be introduced into the atomic models, as an exposure-dependent occupancy of sorts. However, this would require refinement programs to use individual observations as data rather than combined reflections, effectively integrating scaling into refinement. Is there any talk of doing this? I think the hardware could reasonably handle this now? And, besides the question of radiation damage, isn't it perhaps reasonable to integrate scaling into refinement now anyway, since the constraints of hardware are so much lower? Jacob -- ******************************************* Jacob Pearson Keller Northwestern University Medical Scientist Training Program email: [email protected] *******************************************
