[Pw_forum] Consulting for the calculation of band structure with pwscf

Ari P Seitsonen Ari.P.Seitsonen at iki.fi
Sat May 7 14:15:28 CEST 2016

Hello ???, [no affiation, not even name;
  http://www.quantum-espresso.org/forum/#1.0, "Sign your post with your name and affiliation."]

   Adding to the comment of Ridwan Agbaoye, I also agree that I did not 
fully understand for what you meant; I would at least specify the units of 
the k points in the calculation of the bands. Maybe you mean why no 
symmetries are found to each band (or, all bands have the simple 
representation 'A'), or that there are no degeneracies in the bands?

   To start with, did you look at the output of the self-consistent run? I 
tried your file (with reduced number of k points, to make it faster), and 
I see

       2 Sym. Ops., with inversion, found

I would have expected to see more, maybe there is a reason to that? 
Further down,

      Forces acting on atoms (Ry/au):

      atom    1 type  2   force =     0.07295436    0.11942494   93.95848463
      atom    2 type  2   force =    -3.83545650    9.13148686  -74.40161511
      atom    3 type  2   force =    -0.07295436   -0.11942494  -93.95848463
      atom    4 type  2   force =     3.83545650   -9.13148686   74.40161511
      atom    5 type  1   force =     6.08077747  -11.27416034  -50.44274724
      atom    6 type  1   force =    -6.08077747   11.27416034   50.44274724

      Total force =   185.313058     Total SCF correction =     0.000351

      entering subroutine stress ...

           total   stress  (Ry/bohr**3)                   (kbar)     P=********
    1.36208034   0.77578489  -0.05878813     200368.90 114121.88  -8648.03
    0.77578489   2.34432579   0.10345704     114121.88 344862.17  15219.05
   -0.05878813   0.10345704   4.69893799      -8648.03  15219.05 691237.53

These are astronomically large values, something must be wrong in your 
structure. Did you try to visualise your initial structure? (keyword 
"XCrysDen", for example)  They look wrong to me - maybe you got confused 
with the default units of the coordinates in 'pw.x'? Going to crystal 
coordinates looks more like it (there are also more symmetries, which 
usually means more physical structure). Still the atoms look to be very 
close - do you know what the units of length are when specifying 
'celldm()'? I tend to use 'a'/'b'/'c' for this reason - even if the 
meaning of 'celldm(2:6)' is different.

   Maybe those will help; after that I would still spend some time trying 
to understand what is the _expected_ symmetry group, and why you might 
have fewer symmetries than that (some further hint: "verbosity = 'high'" 
to have more output, also including longer output of the symmetry 
operations; and then the number of digits for the coordinates).

   And after these exercises, I wonder why you have coordinates 0.36 for a 
kpoints - is quite close to 1/3 though... ;)

     Good Luck and Happy QE'ing,


PS^1 I still do not understand why people want to run hexagonal cell with 
laterally shifted k points in self-consistent calculations. :)  Well, up 
to them

PS^2 I consider using "outdir = '.'" quite confusing, I would recommend 
you to use some specific directory (my favourite choice is './scratch/', 
which on computers with a dedicated/faster disc space is a symbolic link 
to that file system)

   Ari Paavo Seitsonen / Ari.P.Seitsonen at iki.fi / http://www.iki.fi/~apsi/
     Ecole Normale Supérieure (ENS), Département de Chimie, Paris
     Mobile (F) : +33 789 37 24 25    (CH) : +41 79 71 90 935

On Thu, 5 May 2016, mpan2 at ncsu.edu wrote:

>       Hi,
> I am trying to calculate the band structure of tungsten sulfide. Aattachments are my input files. I input these
> commands:
>     pw.x <ws2.cry.scf.in> ws2.cry.scf.out
>     pw.x <ws2.cry.band.in> ws2.cry.band.out
>     bands.x <ws2.cry.bands.in> ws2.cry.bands.out
> I understand my k path in the second input file in not symmetric, and I am learning how to generate a symmetric path.
> But to my surprise, the k points in file ws2cry.dat have nothing to do with the k points in the second input file. I
> tried to modify the k points for both input files for multiple times, and I found the k points of ws2cry.dat depends on
> the first input file only, with some additionally points generated by ESPRESSO to satisfy symmetry. Besides, there are
> 26 bands in ws2cry.dat, which is different from my setting where nbnd = 28.
> I tried the band structure of fcc Cu before, and the k points in my dat file are identical with those in the band input
> file. I do not understand why it does not work for ws2.
> I am a beginner, and I really need your help. Please forgive me if you think my questions are too silly.
> Thank you for your help, and I am really looking forward to your reply.
> ______________________________________________________________________________________________________________________________

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