Re: [Spglib-users] Determine spacegroup given symmetry operations

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

Hi Keith,

I could find my time to concentrate on working on this feature.

It's in the develop branch in github spglib repository. The tentative
function name is spg_get_hall_number_from_symmetry.
The tentative function definition is found here.
https://github.com/atztogo/spglib/blob/develop/src/spglib.h#L231
By this function, hall_number is obtained. More space group type
information is obtained by spg_get_spacegroup_type with this number.

I haven't implemented the Fortran wrapper but the python wrapper is
done. I ran some test by the following script,

https://github.com/atztogo/spglib/blob/develop/python/test/test_hall_number_from_symmetry.py

In this script, symmetry operations are searched from a crystal
structure and they are used to search space group type as Hall number
(this name t is not defined in crystallography, but a nick name used
in spglib). Then this script checks consistency between Hall number in
the symmetry search from the crystal structure and hall number from
this new function.

In my test, one crystal structure failed in the consistency check, but
all others passed. I mean I hope nomal cases are to be well handled.
The failed one is a distorted crystal structure, which is a naive case
in symmetry handling, i.e., obtained symmetry operations are
numerically distorted, too. Currently I don't have enough amount of
experience around tolerance in this new function, and I have no idea
how to make it more robust, but there would be a solution found in the
future, I hope.

Togo

On Wed, Apr 6, 2016 at 11:27 PM, Atsushi Togo <atz...@gm...> wrote:
> Hi,
>
> It's a nice feature.
>
> If the symmetry operations and lattice parameters are those for the
> primitive cell, it will be very easy (I supposed this case before). If
> not, some more implementation is necessary. But in principle, as an
> input, lattice parameters are unnecessary. I will think.
>
> Togo
>
> On Wed, Apr 6, 2016 at 6:01 PM, Keith Refson <kr...@gm...> wrote:
>> Hi,
>>
>> I'd like to pick up on a question I raised a couple of years ago, as an
>> enhancement
>> to the spglib API.
>>
>> The functionality I need is to pass a lattice and set of symmetry operations
>> as input parameters and obtain the space group - for example as an
>> SpglibDataset.
>> Specifically the atomic co-ordinates are NOT to be used to determine the
>> symmetries.
>>
>> The reason for this is for use in electronic structure codes in the
>> presence of symmetry-breaking.
>> It is commonly necessary to work in a subgroup, where the symmetry is
>> broken by, for example,
>> a magnetic structure, an anisotropic external stress or an electric
>> field or atomic displacement
>> perturbation, or a supercell where the supercell lattice vectors do not
>> transform invariantly under
>> the full point group.  The idea is that the caller works out the
>> remaining symmetries belonging to the
>> subgroup and passes these as input.
>>
>> Following your hint and looking at the code, this does not look
>> difficult in principle.  But there are
>> API design issues which I don't feel qualified to make.  And for
>> maintenance reasons it would be
>> best if any change was incorporated into future spglib releases.
>>
>> Is it realistic to request an enhancement to spglib to do this?
>>
>> sincerely
>>
>> Keith Refson
>>
>>
>> On 27/03/14 04:44, Atsushi Togo wrote:
>>> 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.
>>
>>
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>
>
>
> --
> Atsushi Togo
> Elements Strategy Initiative for Structural Materials, Kyoto university
> E-mail: atz...@gm...



-- 
Atsushi Togo
Elements Strategy Initiative for Structural Materials, Kyoto university
E-mail: atz...@gm...