...
2.Sometimes I found that while searching for anomalous scatterer with
SHELXD which give the coordinates of the scatterer in PDB format with
occupancy more than 1. Why anomalous occupancy may be more than 1.
Not having other wavelengths measured (in contrast with MAD
experiments), there is no way to refine independently anomalous
scatterers' occupancies and the imaginary component of their atomic
structure factors (f''). So, most probably when you end up refining >1
occ's (physically awkward indeed), you're getting the info that the
input f'' should be refined to a lower value (perhaps not the tabulated
one : near-edge values can vary significantly owing to local
environment, anisotropy, oxydation state, etc) - of course this is also
the case when occupancies are less then 1, it's just that you don't look
at it with the same attention. For anomalous scatterer substructure
refinement purposes, anyway it's not a problem to leave occupancies
higher than one (mathematically, it will play just the same role as
reducing f'') (please correct me if I'm wrong here!)
one evident mistake at the end of that : it should read "...the same
role as increasing f'' "
The "please correct me..." is still valid though!!
--
Alejandro Buschiazzo, PhD
Research Scientist
Laboratory of Protein Crystallography
Pasteur Institute of Montevideo
Mataojo 2020
Montevideo 11400
URUGUAY
Phone: +5982 5220910 int. 120
Fax: +5982 5224185
