There does indeed appear to be a tendancy for the SHELXC values to become
slightly negative at the high resolution end, i.e. when a value of zero would
be expected for pure noise, so maybe it is something more fundamental?!
I think it is something more fundamental, and I've just explored
Not to harp on this too much, but I was helping a colleague today on an
unrelated structure, and his dataset also showed negative CCanom's in all bins.
I am now suspecting that there might be an actual bug in Aimless. Anyone else
also seeing this?
Jacob
Vonrheim, or it
may have to do with scaling. Can't figure it out just yet. I am, of course,
assuming that the signs are not random.
Jacob
-Original Message-
From: Keller, Jacob
Sent: Thursday, July 16, 2015 9:46 PM
To: Keller, Jacob; CCP4BB@JISCMAIL.AC.UK
Subject: RE: [ccp4bb] Negative
@JISCMAIL.AC.UK
Subject: Re: [ccp4bb] Negative CCanom
Am 17. Juli 2015 00:00:11 MESZ, schrieb Keller, Jacob
kell...@janelia.hhmi.org:
Jacob's case is twinning in P3(2)12 making the data appear as P6(2)22,
so it is indeed a rotation by 180°.
Yes, this all fits together nicely. If I understand
No, it's just merohedral - the true and the apparent spacegroup belong to the
same pointgroup.
Even if it were pseudo-merohedral it would be a superposition of reflections,
with addition of their intensities.
Well, if there are several apposed crystals as hypothesized before, where they
are
[Sorry, typography was off a bit in the last one]
Here is the answer, I think, to why twinning leads to negative CCanom:
In fact, in any case in which the anomalous signal changes as a function of
exposure, CCanom can be negative.
The usual case is radiation damage:
Consider, to start, four
Jacob's case is twinning in P3(2)12 making the data appear as P6(2)22, so it
is indeed a rotation by 180°.
Yes, this all fits together nicely. If I understand correctly, this would make
my crystals a blend of mero- and pseudo-mero-hedral, so involving I's and F's,
no?
JPK
Here is the answer, I think, to why twinning leads to negative CCanom:
In fact, in any case in which the anomalous signal changes as a function of
exposure, CCanom can be negative.
The usual case is radiation damage:
Consider, to start, four independent measurements of one reflection, two I+
