[QE-users] Structure with symmetry

Thu Mar 18 14:34:30 CET 2021

Hi Giovanni and Quantum Espresso friends,

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

You are right, by specifying the unit cell in the following
way, the warning message disappeared.

<snip>
...
   ibrav            = 8
   celldm(1)        = 10.6279
   celldm(2)        = 1.5
   celldm(3)        = 4.5961940777125589086
…
</snip>

Though, I specified the cell dimensions in Bohr units, but this is 
just a detail for this communication.

As bonus, I can now find the following in the output:

<snip>
...
     point group C_i (-1)   
     there are  2 classes
     the character table:

       E     i    
A_g    1.00  1.00
A_u    1.00 -1.00

     the symmetry operations in each class and the name of the first element:

     E        1
          identity                                               
     i        2
          inversion                                          
…
</snip>

I wonder whether this is compatible to the following output, obtained in the old fashioned way.

<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 10:13, Giovanni Cantele <giovanni.cantele at spin.cnr.it> wrote:
> 
> Here, a list of the ibrav values that you can choose
> https://www.quantum-espresso.org/Doc/INPUT_PW.html#idm200 <https://eur02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.quantum-espresso.org%2FDoc%2FINPUT_PW.html%23idm200&data=04%7C01%7C%7C7db3d1168d674e9bc47b08d8e9ee7e1a%7C9e2777ed82374ab992782c144d6f6da3%7C0%7C1%7C637516557853981073%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=6NM1WCXt2ogavB5wbKfDwv1wmeybmvhrmyyh2PPpEnM%3D&reserved=0>
> 
> It seems that you have a simple orthorhombic lattice, that should correspond to ibrav = 8.
> Than you can specify the variables
> a
> b
> c
> as crystal axes lengths in Angstrom units.
> 
> Giovanni
> 
> 
>> On 18 Mar 2021, at 10:03, Offermans Willem <willem.offermans at vito.be <mailto: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 <mailto:Willem.Offermans at Vito.be>
>> <vito.jpg>
>> 
>> _______________________________________________
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> -- 
> 
> Giovanni Cantele, PhD
> CNR-SPIN
> c/o Dipartimento di Fisica
> Universita' di Napoli "Federico II"
> Complesso Universitario M. S. Angelo - Ed. 6
> Via Cintia, I-80126, Napoli, Italy
> e-mail: giovanni.cantele at spin.cnr.it <mailto:giovanni.cantele at spin.cnr.it>
> Phone: +39 081 676910
> Skype contact: giocan74
> 
> ResearcherID: http://www.researcherid.com/rid/A-1951-2009
> Web page: https://sites.google.com/view/giovanni-cantele/home <https://eur02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fsites.google.com%2Fview%2Fgiovanni-cantele%2Fhome&data=04%7C01%7C%7C7db3d1168d674e9bc47b08d8e9ee7e1a%7C9e2777ed82374ab992782c144d6f6da3%7C0%7C1%7C637516557853991067%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=3LwrKsdaE9ol%2BicjrppzmUrVfumjyQ%2BOw%2Bm%2FAd2fIMo%3D&reserved=0>
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