[QE-users] k-points grid with spin-orbit and non-collinear magnetism

[Pietro Delugas]

Dear Malte

This is also a good place for asking, thanks for that.

It is always a good think to check and have a clear idea of how things 
are working.

First thing to check the results in the two cases; do they match ?

If this is the case, to understand what is happening you  could look at 
the symmetries that the program finds in your system; they are always 
printed out in the xml file. You should find operations for which t_rev 
has a true value, meaning that that operation is usable only together  
with the time reversal operation  and others, for which has a false 
value; these operations do not require the time reversal and only these 
will  be applied  when  you do not let the program to use the  the t_rev 
operation setting no_t_rev to true.

best regards

Pietro



On 09/04/20 09:32, Malte Sachs wrote:
> Dear Pietro,
>
> thank you for your answer. I thought if there is no time reversal 
> symmetry also the combinations with other symmetry operations should 
> be forbidden. Then it is quite similar to e.g. screw axes with a 
> combination of rotation+translation although there don't need to be a 
> rotation present?
> My system is orthorhombic. So the twofold axis plus time reversal 
> leave the spin direction unchanged, right? Question marks started by 
> comparing QE with the LAPW-code Elk. In the Elk code it seems that 
> rotation+time-reversal is not used for k-point reduction. However, 
> this should then be a question for the Elk forum....
>
> Best regards,
> Malte
>
> Am 08.04.20 um 16:57 schrieb Pietro Delugas:
>>
>> Dear Molte
>>
>> your system could be symmetric under operations  made by a rotation + 
>> the time reversal operation, in fact these are  the operations that 
>> the no_t_rev option disables, not the time reversal per se.
>>
>> does  the results  with and without t_rev compare correctly ?
>>
>> best regards Pietro
>>
>> On 08/04/20 12:57, Malte Sachs wrote:
>>> Dear all,
>>>
>>> I am performing non-collinear magnetic calculations with spin-orbit 
>>> interactions with QE 6.5. As far as I have understand, for a 
>>> ferromagnetic system time-reversal symmetry should be broken in this 
>>> case.
>>>
>>> Although the program detects the right magnetic double point group, 
>>> the k-points grid is set up with time-reversal symmetry and I have 
>>> to set the no_t_rev flag manually to disable this. Is there any 
>>> reason why this isn't done by default (e.g. these calculations can 
>>> be done safely with a more reduced k-points grid...)? Do I miss 
>>> something?
>>>
>>> Best regards,
>>>
>>> Malte Sachs
>>>
>>>
>>>
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>>
>> _______________________________________________
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>
>
> -- 
> Malte Sachs
> Anorganische Chemie, Fluorchemie
> Philipps-Universität Marburg
> Hans-Meerwein-Straße 4
> 35032 Marburg (Paketpost: 35043 Marburg)
> Tel.: +49 (0)6421 28 - 25 68 0
> http://www.uni-marburg.de/fb15/ag-kraus/
>
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso)
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