[QE-users] Symmetry Considerations

[Paolo Giannozzi]

Quick google search: http://quantum.phys.cmu.edu/groupth/gt21.pdf

On Fri, Jan 11, 2019 at 10:23 AM Offermans Willem <willem.offermans at vito.be>
wrote:

> Sorry for my ignorance, but I still don’t see the point.
>
> Maybe a reference to some literature might help.
>
>
> Met vriendelijke groeten,
> Mit freundlichen Grüßen,
> With kind regards,
>
>
> Willem Offermans
> Researcher Electrocatalysis SCT
> VITO NV | Boeretang 200 | 2400 Mol
> Phone:+32(0)14335263 Mobile:+32(0)492182073
>
> Willem.Offermans at Vito.be
>
>
> On 11 Jan 2019, at 09:58, Malte Sachs <malte.sachs at chemie.uni-marburg.de>
> wrote:
>
> Dear Willem,
>
> in case of a screw axis or a glide plane you couple a rotation or a mirrow
> with a fractional translation (e.g. 1/2 or 1/3 of a lattice vector).
>
> Best,
> Malte
>
>
> Am 11.01.2019 um 09:03 schrieb Offermans Willem:
>
> Dear Paolo and Quantum Espresso friends,
>
> I’m sorry, but your explanation did not enlighten me.
>
> Your response: "it means that the symmetry operation consists in a
> rotation (or a rotation + spatial inversion) plus a translation (not a
> lattice one)” don’t ring a bell.
>
> What kind of translational symmetry are you talking about, if not the
> lattice one?
>
> My system has S2-Symmetry. This means a rotation about 180°, followed by
> reflection in a plane perpendicular to the rotation axis. It can be
> shortened to an inversion centre. Combined with the identity operation,
> this leads to 2 Sym.Ops, which have been detected by the program. This is
> consistent with the message in the output. Since I’m dealing with a slab,
> the system also has translational symmetry. I don’t see why the inversion
> centre should be incommensurate with this translational symmetry.
>
> What is the connection to the FFT grid?
>
>
>
>
>
> Met vriendelijke groeten,
> Mit freundlichen Grüßen,
> With kind regards,
>
>
> Willem Offermans
> Researcher Electrocatalysis SCT
> VITO NV | Boeretang 200 | 2400 Mol
> Phone:+32(0)14335263 Mobile:+32(0)492182073
>
> Willem.Offermans at Vito.be
>
> <vito.jpg>
>
> On 10 Jan 2019, at 22:00, Paolo Giannozzi <p.giannozzi at gmail.com> wrote:
>
> On Thu, Jan 10, 2019 at 4:30 PM Offermans Willem <willem.offermans at vito.be>
> wrote:
>
>      2 Sym. Ops., with inversion, found ( 1 have fractional translation)
>> [...] What does it mean?
>>
>
> it means that the symmetry operation consists in a rotation (or a rotation
> + spatial inversion) plus a translation (not a lattice one)
>
> At some point in the sequence of calculations, the output contained the
>> following message about symmetry:
>>
>>     No symmetry found
>>
>> I was surprised about the lost of symmetry. Is it related to the
>> fractional translation?
>>
>
> no, unless this happens in the last scf step, in which the FFT grid may
> change, in which case this is what may happen:
>
>           (note:  1 additional sym.ops. were found but ignored
>            their fractional translations are incommensurate with FFT grid)
> Paolo
> --
> Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
> Phone +39-0432-558216, fax +39-0432-558222
>
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-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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