Hi
I'd run the reflection file through pointless rather than rely on
cell dimensions and/or systematic absences. This is a quick and easy
test to do and more reliable. As Bert suggests, the only real way to
know the symmetry is after successful structure solution and
refinement (but even then you can be fooled...).
On 8 Jul 2011, at 21:07, Van Den Berg, Bert wrote:
I'd say its very likely to be orthorhombic. Refinement should tell
you.....its the best way to determine the space group anyway. Why
do you doubt its orthorhombic? Is Vm reasonable?
It could be monoclinic and merohedrally winned with the beta angle
very close to 90 degrees, but my money is on orthorhombic. if
refinement fails I would try monoclinic plus/minus twinning. As for
the operators, xxxxxx.triage will tell you and xxxxxx.refine will
apply them for you during refinement....;-)
Bert
________________________________________
From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] On Behalf Of Raji
Edayathumangalam [r...@brandeis.edu]
Sent: Friday, July 08, 2011 3:24 PM
To: CCP4BB@JISCMAIL.AC.UK
Subject: Re: [ccp4bb] Potential Space Group Issue
Oops sorry for the slippery fingers. I meant h00, 0k0 and 00l in my
original email and NOT "00h, 00k, 00l". Note the correction
especially if you are a first-year graduate student trying to learn
stuff from these emails :)
Raji
On Thu, Jul 7, 2011 at 11:30 PM, Raji Edayathumangalam
<r...@brandeis.edu<mailto:r...@brandeis.edu>> wrote:
Hello Everyone,
I have a 3.1 Ang dataset for which I'd like to get to the bottom of
what the correct space group is.
The current unit cell in p212121 is 98.123 101.095 211.201
90.000 90.000 90.000
I fed the reflection data into Xtriage to look for twinning and
pseudotranslational NCS and there is no indication for either issue
in the Xtriage output. Also, all odd 00h, 00k, 00l reflections are
systematically absent as they should be for p212121.
However, my colleague who is also working on the same dataset
recently reprocessed the data in P21. Here's the cell in p21:
98.010 100.940 210.470 90.00 90.04 90.00 p21
I am not sure if BETA=90.04 is significant enough to treat as p21
(0.04% deviation of beta angle from ideal lattice for p212121). I
don't think so but I could be wrong. Could someone please clarify?
Also, what kind of twinning and twinning operators can relate a
p212121 cell to a p21 cell with almost identical unit cell
parameters as that of the p212121 cell and leave all systematic
absences intact?
Thanks much.
Raji
-----------
Raji Edayathumangalam
Instructor in Neurology, Harvard Medical School
Research Associate, Brigham and Women's Hospital
Visiting Research Scholar, Brandeis University
--
----------------------
Raji Edayathumangalam
Instructor in Neurology, Harvard Medical School
Research Associate, Brigham and Women's Hospital
Visiting Research Scholar, Brandeis University
Harry
--
Dr Harry Powell,
MRC Laboratory of Molecular Biology,
Hills Road,
Cambridge,
CB2 0QH
