On Fri, May 16, 2014 at 7:12 AM, <[email protected]> wrote: > Short of storing images, which is the ultimate preservation of primary > information, I have always been puzzled by the fact that the PDB only > stores > unique reflections i.e. no Friedel pairs even when provided. Is this > outdated > perhaps ? I remember that my deposited SFs in the past where reduced to not > contain Friedel pairs. If there had been a concern about increasing the > storage space by actually less than twice the space for unique SFs, this > may > be invalid today and is still far less than the space required for images. > However, it is possible that the information content in Friedel pairs is > deemed insignificant compared to their extra costs. I for one would > appreciate > having access to Friedel pairs very much. >
They definitely store Friedel pairs! Maybe you're confused by the layout of the mmCIF file, which (like MTZ) usually lists just the unique (non-anomalous) indices, but with separate values for F+/F- when they are available. I've been making extensive use of anomalous data depositions - unfortunately there aren't as many as we would like, either because many people do not realize that this is useful information even when the experiment was not specifically looking for anomalous signal, or because the complexity of PDB deposition discourages providing the most complete data. An even more useful improvement would be to make deposition of unmerged intensities straightforward - the JCSG does this somehow but it is non-trivial for the average user. Hopefully this will also change soon. -Nat
