One issue is whether the extra data for the 80% solvent volume consists of independent measurements. The references below suggest that the required "oversampling " of intensities is given when one has a 50% solvent volume.
J. Miao, D. Sayre, and H. N. Chapman, "Phase retrieval from the magnitude of the Fourier transforms of nonperiodic objects," J. Opt. Soc. Am. A 15, 1662-1669 (1998)
Or
Q. Shen<http://scripts.iucr.org/cgi-bin/citedin?search_on=name&author_name=Shen%2C%20Q%2E>, I. Bazarov<http://scripts.iucr.org/cgi-bin/citedin?search_on=name&author_name=Bazarov%2C%20I%2E> and P. Thibault<http://scripts.iucr.org/cgi-bin/citedin?search_on=name&author_name=Thibault%2C%20P%2E> Diffractive imaging of nonperiodic materials with future coherent X-ray sources J. Synchrotron Rad. (2004). 11, 432-438
Of course the above assumes everything is ideal.
Colin
From: CCP4 bulletin board [mailto:[log in to unmask]] On Behalf Of Guangyu Zhu
Sent: 15 March 2013 00:28
To: ccp4bb
Subject: [ccp4bb] Resolution and data/parameter ratio, which one is more important?
I have this question. For exmaple, a protein could be crystallized in two crystal forms. Two crystal form have same space group, and 1 molecule/asymm. One crystal form diffracts to 3A with 50% solvent; and the other diffracts to 3.6A with 80% solvent. The cell volume of 3.6A crystal must be 5/2=2.5 times larger because of higher solvent content. If both data collecte to same completeness (say 100%), 3.6A data actually have higher data/parameter ratio, 5/2/(3.6/3)**3= 1.45 times to 3A data. For refinement, better data/parameter should give more accurate structure, ie. 3.6A data is better. But higher resolution should give a better resolved electron density map. So which crystal form really give a better (more reliable and accurate) protein structure?
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