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<[log in to unmask]> 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:[log in to unmask]] On Behalf Of Theresa Hsu
>> Sent: Friday, July 27, 2012 12:54 PM
>> To: [log in to unmask]
>> 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.
>