Are all the software packages consistent in their (mis)use of these
symbols? Recently I scaled data (scalepack) as R3, imported to ccp4 as H3,
and had to make a link in $ODAT/symm from R32 to H32 (which it turned out to
be).
Ian Tickle wrote:
If we're all agreed that ITC(A) is taken as the authority on all
matters of space group symbology (and I for one certainly agree that
it should be), then SG symbol H32 (SG #145:
http://img.chem.ucl.ac.uk/sgp/medium/145bz1.htm) has nothing to do
with R32 (SG #155: http://img.chem.ucl.ac.uk/sgp/medium/155az1.htm)!
According to the Hermann-Mauguin system of nomenclature H32 (more
correctly written as H3_2 where the '_' indicates a subscripted screw
axis) would be the hexagonal-centred (H) lattice setting of P32 (P3_2
in H-M). H32 as an alternate setting symbol for R32 is a very recent
PDB invention which conflicts with the well-established H-M convention
used throughout ITC. The ITC symbols for the rhombohedral& hexagonal
axis settings of SG R32 are R32:r and R32:h respectively, i.e. obvious
extensions of the H-M symbols without introducing any conflict with
the existing convention, as the PDB symbol does. The confusion has
arisen from the failure to distinguish the lattice type (the first
letter of the symbol) from the symbol for the basis system of the
setting (the final letter after the ':').
See http://cci.lbl.gov/~rwgk/my_papers/CCN_2011_01_H3_H32.pdf for an
excellent explanation of all this and of the confusion that arises
when programmers ignore established conventions and 're-invent the
wheel' (e.g. SCALEPACK apparently swaps the meaning of the PDB symbols
R32& H32 and uses R32 for PDB H32 and vice-versa!).
Cheers
-- Ian
On 27 July 2012 21:09, Bernhard Rupp<hofkristall...@gmail.com> wrote:
H32 indicates the hexagonal obverse setting (as you list) for a R centered trigonal
cell, which is 3x larger than the primitive R32 cell indexed a=b=c, al=be=ga<>
90. Standard imho is the H32 setting, for which I will probably get flamed.
The relation between H and R cells is depicted here:
http://www.ruppweb.org/Garland/gallery/Ch5/pages/Biomolecular_Crystallography_Fig_5-29.htm
This has been discussed and is explained in the ccp4 tutorials and doc afaik,
where you can find more detailed info.
For proper format in a journal, I would suggest to adhere to the format given
in the ITC (International tables for Crystallography), I.e. Bravais Italic,
subscripted screw symbols. Note that this is not the format you put it into
most programs - their docs help.
You can also try my old space croup decoding program to see general positions,
operators, matrices and other useful stuff.
http://www.ruppweb.org/new_comp/spacegroup_decoder.htm
HTH, BR
-----Original Message-----
From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Theresa
Hsu
Sent: Friday, July 27, 2012 12:54 PM
To: CCP4BB@JISCMAIL.AC.UK
Subject: [ccp4bb] Space group R32 and H32
Dear all
I have a confusion on the space group R32 and H32. For a cell parameter of a =
b not equal to c, alpha=beta, not equal to gamma, is it considered as R32 or
H32?
I tried searching the mail list archives but it does not help a beginner
crystallographer like me.
I also have another basic question. What is the correct way for writing space
groups? Is the Bravais lattice in italic and is there space after that? Or it
does not matter because both are used in literature?
Thank you.
