Well - first use pointless to see if there is any agreement between the
two data sets. You can input the unmerged scalepack output..
Use the option - find Laue group for each data set - it will suggest if
you should have point group 222 or just 2.
And then the option.
match index to reference and again it will suggest how to reindex the
data to get a better agreement..
The reindexing has to be k,h,-l in fact to get the cells to agree which
means the spacegroup cant be P21 but it seems much more likely the point
group IS P222..
Finding twin operators when you have assigned the wrong spacegroup can
be tricky.
Re the lower FreeR - were you careful to maintain the 222 symmetry of
the FreeR assignment? If not and if the point group really is 222 then
the FreeR can be misleading.
And again if you now have doubled the number of "independent" molecules
in the asymmetric unit the r factors will usually fall..
Eleanor
Yuan Cheng wrote:
Hi everyone,
I have some question about the merging of diffraction data from
different crystals. I have two (room-temperature) datasets in my hand
and each of them can be scaled in P21 space group and the screw axis
is along k. However,each dataset only have below 55% completeness. To
get better completeness, I am trying to merge this two datasets. The
problem is one dataset has cell dimension
(80.632,87.085,114.977),(90,90.026,90) and the other one has
(85.497,79.857,114.003) (90,90.004,90),. It looks like that the a,b
dimensions are switched between these two datasets. Unsurprisingly,the
chi^2 is very high when I tried to merge these two datasets in
scalepack.I am wondering whether there is any way to reindex these two
datasets to make their a/b dimensions match. Any suggestion will be
highly appreciated.
By the way, as you might notice, the beta angle is pretty close to
90 degree. I scaled the datasets into P212121 or P2221 or P21212 at
the beginning,I had no trouble to merge them in these space groups.
However,I could not make the Rfree go below 45% during following
refinement (2.7 angstrom cutoff). Phenix.xtriage indicated that there
might exist twinning but no twin law is given. Then I reindexed the
data into P2 and scaled them in P21 SG.Phenix.xtriage indicates there
exists a pseudomerohedral twinning operator. When I used the twin law
given in phenix.refine,the Rfree could go down to 29%. So I think P21
might be the correct space group.
Thanks again for any suggestion.
Yuan
