Yambo Community Forum

Posted: **Tue Dec 16, 2025 8:19 pm**

Hi all,

What are the conventions for how yambo prints symmetries in section 02.02?

My material has two magnetically inequivalent atoms at (0,1/3,0) and (0,-1/3,0), specifically labeled as Ni1 and Ni2 in quantum espresso. QE finds two symmetries:

Code: Select all

      isym =  1     identity

 Time Reversal            0
 cryst.   s( 1) = (     1          0          0      )
                  (     0          1          0      )
                  (     0          0          1      )

 cart.    s( 1) = (  1.0000000  0.0000000  0.0000000 )
                  (  0.0000000  1.0000000  0.0000000 )
                  (  0.0000000  0.0000000  1.0000000 )


      isym =  2     180 deg rotation - cart. axis [0,1,0]

 Time Reversal            1
 cryst.   s( 2) = (    -1          0          0      )
                  (     0          1          0      )
                  (     0          0         -1      )

 cart.    s( 2) = ( -1.0000000  0.0000000  0.0000000 )
                  (  0.0000000  1.0000000  0.0000000 )
                  ( -0.0000000  0.0000000 -1.0000000 )

Yambo (version 5.1.0) also finds two symmetries, but it seems to flip the sign of the second one:

Code: Select all

   [S 1]:  1.000000  0.000000  0.000000  0.000000  1.000000  0.000000  0.000000  0.000000  1.000000
   [S*2]:  1.000000  0.000000  0.000000  0.000000 -1.000000  0.000000  0.000000  0.000000  1.000000

As you can see, there is an overall sign difference between the symmetry found by QE vs Yambo. Does the * in S*2 indicate that the symmetry should be multiplied by -1?

Best,
Miles

Posted: **Wed Dec 17, 2025 1:23 pm**

Dear Miles,

have you checked how the lattices vector are reported in QE and Yambo? It is possible they are different and the overall picture of the symmetry is equivalent.

Best,

Daniele

Posted: **Thu Dec 18, 2025 11:31 pm**

Ah I think the difference was just due to time reversal, so yambo was displaying the symmetry operation on k-space.

Posted: **Sun Dec 21, 2025 3:06 pm**

Dear Miles,

this should be reported in the report file. TR symmetry are not listed but it is stated if they are included.

Best,
Daniele

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