Re: [Spglib-users] symmetrizing positions/cell vectors without altering cell?

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

You can obtain more information by spg_get_dataset:
https://atztogo.github.io/spglib/api.html#spg-get-dataset-and-spg-get-dataset-with-hall-number

Togo

On Sat, Dec 16, 2017 at 3:04 AM, Noam Bernstein
<noa...@nr...> wrote:
>> On Dec 14, 2017, at 7:31 PM, Atsushi Togo <atz...@gm...> wrote:
>>
>> No.
>>
>> Cell vectors follow the crystallographic point group (multiplied with
>> translation group). But if I remember correctly, simple application of
>> these symmetry operations similarly to the points of atoms didn't work
>> well. So my strategy is that using the constraints of Bravais lattice
>> for angles and equivalent basis vector lengths to symmetrize the basis
>> vectors. For distorted basis vectors, it's not uniquely defined the
>> directions of basis vectors in Cartesian coordinates, I employed a
>> strategy to align those basis vectors to the Cartesian axes as shown
>> in the spglib documentation. If you want to rotate basis vectors to be
>> along some directions, you can do rotate back afterwards using the
>> rotation matrix calculated from the initial and final basis vectors
>> and the transformation matrix given from spglib. In summary, to
>> symmetrize basis vectors, there is large freedom to make it, and it
>> can be dependent on users' will, so I don't want to provide a function
>> that does too much.
>
> That sounds reasonable, except that I can’t figure out how to decompose
> the transformation from my original vectors to the symmetrized vectors into
> a supercell+deformation part and a rotation.  standardize_cell just returns
> a set of final lattice vectors. Is that separation already someplace in the code,
> or do I need to decompose the transformation matrix myself somehow?
>
>                                                                 Noam



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