[Pw_forum] some band parities absent at bands.x output

[Rajdeep Banerjee]

Dear QE users,
                      I am working on a 2D system which has inversion
symmetry (I also checked the scf output). I wanted to see the parities of
the bands at the time reversal invariant momenta (TRIM) points by using
lsym = .true. in the input of bands.x. I found that some of the parities
are not written (*'?' marks*) at the output e.g. I am attaching the result
for the \Gamma point of the Brillouin zone:

 **************************************************************************

                    xk=(   0.00000,   0.00000,   0.00000  )

     double point group C_i (-1)
     there are  4 classes and  2 irreducible representations
     the character table:

       E     -E    i     -i

G_2+   1.00 -1.00  1.00 -1.00
G_2-   1.00 -1.00 -1.00  1.00

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

     E             1

     -E           -1

     i             2

     -i           -2


     Band symmetry, C_i (-1)    double point group:

     e(  1 -  2) =    -26.22720  eV     2   -->   2 G_2+
     e(  3 -  4) =    -26.22052  eV     2   -->   2 G_2-
     e(  5 -  6) =    -26.16497  eV     2   -->   2 G_2+
     e(  7 -  8) =    -26.15690  eV     2   -->   2 G_2-
     e(  9 - 10) =    -25.65055  eV     2   -->   2 G_2+
     e( 11 - 12) =    -25.64216  eV     2   -->   2 G_2-
     e( 13 - 14) =    -25.61619  eV     2   -->   2 G_2+
     e( 15 - 16) =    -25.60915  eV     2   -->   2 G_2-
     e( 17 - 18) =    -25.56476  eV     2   -->   2 G_2+
     e( 19 - 20) =    -25.55818  eV     2   -->   2 G_2-
     e( 21 - 22) =    -19.83112  eV     2   -->   2 G_2+
     e( 23 - 24) =    -19.82338  eV     2   -->   2 G_2-



*    e( 25 - 26) =    -17.12502  eV     2   -->   ?     e( 27 - 28) =
-17.12324  eV     2   -->   ?     e( 29 - 30) =    -17.09245  eV     2
-->   ?     e( 31 - 32) =    -17.09133  eV     2   -->   ?*
     e( 33 - 34) =    -12.20984  eV     2   -->   2 G_2+
     e( 35 - 36) =    -12.09999  eV     2   -->   2 G_2-
     e( 37 - 38) =    -10.28999  eV     2   -->   2 G_2+
     e( 39 - 40) =     -8.62971  eV     2   -->   2 G_2-
     e( 41 - 42) =     -8.22226  eV     2   -->   2 G_2+
     e( 43 - 44) =     -8.20903  eV     2   -->   2 G_2-
     e( 45 - 46) =     -8.13155  eV     2   -->   2 G_2+
     e( 47 - 48) =     -8.11535  eV     2   -->   2 G_2-
     e( 49 - 50) =     -6.09122  eV     2   -->   2 G_2+
     e( 51 - 52) =     -5.86160  eV     2   -->   2 G_2-
     e( 53 - 54) =     -4.79659  eV     2   -->   2 G_2+
     e( 55 - 56) =     -4.75627  eV     2   -->   2 G_2-
     e( 57 - 58) =     -4.72655  eV     2   -->   2 G_2+
     e( 59 - 60) =     -4.67253  eV     2   -->   2 G_2-
     e( 61 - 62) =     -4.65292  eV     2   -->   2 G_2+
     e( 63 - 64) =     -4.62364  eV     2   -->   2 G_2-
     e( 65 - 66) =     -3.53630  eV     2   -->   2 G_2+
     e( 67 - 68) =     -3.37897  eV     2   -->   2 G_2+
     e( 69 - 70) =     -3.37099  eV     2   -->   2 G_2-
     e( 71 - 72) =     -3.26680  eV     2   -->   2 G_2-
     e( 73 - 74) =     -3.15149  eV     2   -->   2 G_2+
     e( 75 - 76) =     -2.28433  eV     2   -->   2 G_2-
     e( 77 - 78) =     -2.20095  eV     2   -->   2 G_2+
     e( 79 - 80) =     -0.88842  eV     2   -->   2 G_2+
     e( 81 - 82) =      0.19215  eV     2   -->   2 G_2-
     e( 83 - 84) =      1.70887  eV     2   -->   2 G_2-

 **************************************************************************
I want to understand why some of the parities were no written. Any help in
this regards would be highly appreciated. Thanks in advance!


best regards,
-- 
Rajdeep Banerjee
PhD student
JNCASR, Bangalore
India
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