[Cod-bugs] spacegroup name 'C 2 e b'

[Saulius Gražulis]

Hi, Marcin,

On 2024-04-27 14:41, Marcin Wojdyr wrote:
> I've been checking space group names, and I noticed that I can't read
> 'C 2 e b' which is used in COD. I see several space groups were
> renamed in 2015 to introduce 'e':
> https://github.com/cod-developers/cod-tools/commit/173879a3dc289f36b0cb343c9464bb9fdc19ecf4
> but this one name differs from symbols used in cctbx and spglib that
> I've been using as a reference.
> So we have:
> C 2 c b - old
> C 2 c e - cctbx
> C 2 e b - cod-tools
> I didn't even try to understand the details of the space group naming,
> so I can't tell which name is correct. Any thoughts?
>
 From what I see, this could be indeed a bug in our tables, the ITC Vol. 
A to which we all refer indeed mentions 'C 2 c e' and not the 'C 2 e b'. 
We'll have a look and harmonise the space group name with the Tables.

I the meantime, may I suggest that you either use the Hall symbol ('C 
-2ac 2'), which seems to be correct for all 9 COD entries that mention 
'C 2 e b' [1]. I have even a code (in Ada :) that parses the Hall symbol 
and returns symmetry operation matrices [2]. Alternatively, probably the 
most versatile way to describe symmetry is to use symmetry operation 
matrices described in the '_space_group_symop_operation_xyz' data item. 
All entries in [1] seem to have these data items.

Sorry for the inconvenience!

Sincerely,
Saulius

Refs:

[1] COD entries with the 'C 2 e b' H-M space group symbol:

> mysql -u cod_reader -h sql.crystallography.net cod -e 'select file, 
> sgNumber, sg, sgHall, svnrevision, date from data where sg = "C 2 e b" 
> order by file'
> +---------+----------+---------+----------+-------------+------------+
> | file    | sgNumber | sg      | sgHall   | svnrevision | date       |
> +---------+----------+---------+----------+-------------+------------+
> | 4003235 |       41 | C 2 e b | C -2ac 2 |      231452 | 2020-10-21 |
> | 4127236 |       41 | C 2 e b | C -2ac 2 |      223200 | 2020-10-21 |
> | 4131512 |       41 | C 2 e b | C -2ac 2 |      241703 | 2020-10-21 |
> | 4518546 |       41 | C 2 e b | C -2ac 2 |      263581 | 2021-04-04 |
> | 7060405 |       41 | C 2 e b | C -2ac 2 |      263802 | 2021-04-05 |
> | 7225528 |       41 | C 2 e b | C -2ac 2 |      183458 | 2020-10-21 |
> | 7237089 |       41 | C 2 e b | C -2ac 2 |      236814 | 2020-10-21 |
> | 7238091 |       41 | C 2 e b | C -2ac 2 |      244064 | 2020-10-21 |
> | 7701682 |       41 | C 2 e b | C -2ac 2 |      223334 | 2020-10-21 |
> +---------+----------+---------+----------+-------------+------------+

[2] Gražulis, S. (2022) A program and library to decode Hall 
crystallographic space group symbols. GitHub. URL: 
https://github.com/sauliusg/decode-Hall-symbol [accessed 
2024-04-27T15:08+03:00].

-- 
Dr. Saulius Gražulis
Vilnius University Institute of Biotechnology, Saulėtekio al. 7
LT-10257 Vilnius, Lietuva (Lithuania)
fax: (+370-5)-2234367 / phone (office): (+370-5)-2234353
mobile: (+370-684)-49802, (+370-614)-36366

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