Re: [Spglib-users] Introduction and CASTEP

[Atsushi T. <atz...@gm...>]

Hello,

I'm a developer of spglib.

1) I think it's not a very hard work. lattice parameters are necessary
to be supplied for hal_get_hall_symbol, but for this purpose, just
dummy lattice parameters should be OK.
2) If I understand correctly, what usually obtained as symmetry
operations are not a space group, but coset representatives, which may
not form a group in the case of non-symmorphic crystals. For an lxmxn
supercell, spglib returns the coset representatives (or symmetry
operations) x a set of pure translations of lxmxn. In addition, the
point group of the lattice parameters given for the supercell is not
the same as that of primitive cell, then the symmetry is given lower,
i.e. 2x1x1 of cubic is not treated as cubic symmetry x pure
translations, but tetragonal symmetry x pure translations.
3) The symmetry operations are internally compared with database of
space group types, and if the operations can be a space group type,
the tolerance parameter to be used for symmetry operation search is
adjusted (usually only reduced) until the symmetry operations will be
OK.

Best regards,

Togo

On Wed, Mar 26, 2014 at 10:37 PM, Keith Refson <kr...@gm...> wrote:
> Hello,
>
> I would like to introduce myself as one of the developers of the CASTEP
> DFT materials modelling code.   We plan to replace some old space group
> symmetry analysis code with spglib.
>
> My initial tests are proving very positive about the capabilities of
> spglib for this purpose.
>
> 1) There is one piece of missing functionality we need.  This would be
>     a routine similar to spg_get_dataset() but which takes as input a
>     list of symmetry operations, not the lattice and co-ordinates. This
>     would be to analyse a pre-supplied set of operations (rotation
>     matrices and translations).  How hard would it be to add this?
>
> 2) May I ask how spglib handles non-primitive supercells. If,
>     for example you were to pass a lxmxn block of primitive cells would
>     spglib return the complete product group of the translation and
>     rotation groups?  This is important because if only the rotation
>     subset were specified the set of operations do not form a complete
>     group. (As atoms can be mapped between different primitive cells).
>
> 3) Is there any built-in test whether the symmetry operations form a
>     group?
>
> sincerely
>
> Keith Refson
>
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-- 
Atsushi Togo
http://atztogo.github.com/
atz...@gm...