[QE-users] Structure with symmetry

[Offermans Willem]

Dear Giovanni, Lorenzo and Quantum Espresso friends,

Thank you for your responses. It is very much appreciated.

I was not aware of scan_ibrav.x or cell2ibrav.x, maybe the
existence of these tools can be added to the warning message:

<snip>
...
     Message from routine setup:
     using ibrav=0 with symmetry is DISCOURAGED, use correct ibrav instead
…
</snip>

It would offer a useful hint for the user.

Anyway, I somehow solved the issue with the help of Giovanni. Eventually,
it was not very difficult, maybe trivial to most QE users. But being not very 
much trained in crystallography, it was not immediately clear to me. 

The only open issue is with the following message in the output. It is for
the same system with S_2 symmetry. So the point group is C_i.
I guess the find_sym routine was able to figure this out.
If this is the case, I would recommend to add the point group symbol to the 
output. It makes it again much clearer.

<snip>
...
    Found symmetry operation: I + ( -0.5000  0.0000 -0.0000)
     This is a supercell, fractional translations are disabled
     Message from routine find_sym:
     Not a group! Trying with lower acceptance parameter...
     Message from routine find_sym:
     Symmetry operations form a group
…
</snip>

The last line says: "Symmetry operations form a group”.
Great, which group is it?


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 18 Mar 2021, at 17:39, Lorenzo Paulatto <paulatz at gmail.com> wrote:
> 
> Oddly enoughm the scan_ibrav.x little program does not work in your case (I'm fixing it), but cell2ibrav does:
> $ PW/tools/cell2ibrav.x  
> Enter the lattice vectors (one per line)
> 1.000000   0.000000   0.000000
> 0.000000   1.500000   0.000000
> 0.000000   0.000000   4.596194
> Enter alat (or 'x' to skip if axis are in bohr)
> 10.627880
> ibrav =      8
> celldm(1) =     10.62788000
> celldm(2) =      1.50000000
> celldm(3) =      4.59619400
> New lattice vectors in bohr:
>    10.62788000     0.00000000     0.00000000
>     0.00000000    15.94182000     0.00000000
>     0.00000000     0.00000000    48.84779829
> New lattice vectors in old alat:
>     1.00000000     0.00000000     0.00000000
>     0.00000000     1.50000000     0.00000000
>     0.00000000     0.00000000     4.59619400
> New lattice vectors in new alat:
>     1.00000000     0.00000000     0.00000000
>     0.00000000     1.50000000     0.00000000
>     0.00000000     0.00000000     4.59619400
> Discrepancy old/new in bohr =     0.000000
> 
> --
> Lorenzo Paulatto - Paris
> On Mar 18 2021, at 10:03 am, Offermans Willem <willem.offermans at vito.be> wrote:
> 
> Dear Quantum Espresso friends,
> 
> In most of my calculations, I’m dealing with metallic slabs, representing
> surfaces, derived from fcc metals, such as (221) or (533).
> 
> In these calculations, I’m dealing with structures with symmetry.
> The single symmetry element is an inversion center. S_2 is the Schönfließ symbol,
> if I recall correctly. 
> 
> In the output file of pw.x, I encounter the following note:
> 
> <snip>
> ...
>      Message from routine setup:
>      using ibrav=0 with symmetry is DISCOURAGED, use correct ibrav instead
> …
> </snip>
> 
> The unitcell is defined as:
> 
> <snip>
> ...
>      celldm(1)=  10.627880  celldm(2)=   0.000000  celldm(3)=   0.000000
>      celldm(4)=   0.000000  celldm(5)=   0.000000  celldm(6)=   0.000000
> 
>      crystal axes: (cart. coord. in units of alat)
>                a(1) = (   1.000000   0.000000   0.000000 )  
>                a(2) = (   0.000000   1.500000   0.000000 )  
>                a(3) = (   0.000000   0.000000   4.596194 )  
> …
> </snip>
> 
> I would like to follow the advice to use the correct ibrav, but I need some help
> to determine the correct ibrav. 
> 
> Can someone help me to determine the correct Ibrav?
> 
> 
> 
> 
> 
> 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 <https://eur02.safelinks.protection.outlook.com/?url=https%3A%2F%2Flink.getmailspring.com%2Flink%2F2AD46120-DDAD-4F73-91B7-A26C8881CEA0%40getmailspring.com%2F0%3Fredirect%3Dmailto%253AWillem.Offermans%2540Vito.be%26recipient%3DdXNlcnNAbGlzdHMucXVhbnR1bS1lc3ByZXNzby5vcmc%253D&data=04%7C01%7C%7C0ede0550f7e64c0f1cb908d8ea2c6ed8%7C9e2777ed82374ab992782c144d6f6da3%7C0%7C1%7C637516823855682964%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=Lb1wEO%2FKzG2MuJSR0cu%2BfNjiZOLWaKOa%2F4i%2BkQ6528w%3D&reserved=0>
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