[Pw_forum] Having problem with Total energy in Band structure calculation

[Ari P Seitsonen]

Dear Alhassan Shuaibu,

   As already stated in the previous answer, there is a problem in your 
structure: I guess that the coordinates are _not_ given Ångström like 
stated in your input. And the k points, ibrav = 5 would suggest that you 
need a more homogeneous k point sampling in all directions, doesn't it?

   Indeed the cut-off energz is far too low; I don't know these 
elements/pseudo potentials too well, but they might also require an 
ecutwfc of > 100 Ry. Please test carefully (eg forces as a function of the 
cut-off energy etc).

     Greetings,

        apsi

-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-
   Ari P Seitsonen / Ari.P.Seitsonen at iki.fi / http://www.iki.fi/~apsi/
   Institut für Chemie der Universität Zürich, CH-8057 Zürich
   Tel: +41 44 63 54 497  /  Mobile: +41 79 71 90 935


On Sun, 12 Jan 2014, Alhassan Shuaibu wrote:

> Hello
> I am trying to do band structure calculations for Ternary Bi2Te2S.But I am getting a positive TOTAL energy . I have checked my crystal structure with Xcrysden, looks
> okay to me. please is this related to my generated coordinate?
> my INPUT FILE
> &CONTROL
>     calculation='scf'
>     restart_mode='from_scratch',
>     prefix='Bi2Te2SRH_exc1',
>     tstress = .true.
>     tprnfor = .true.
>     pseudo_dir ='/home/alhas/Alhas/espresso-5.0.2/pseudo/' ,
>     outdir='/home/alhas/Alhas/espresso-5.0.2/bin/' ,
>  /
>  &SYSTEM
>                     ibrav =  5,
>                      a = 10.931,
>                      cosab = 0.922901387,
>                      nat = 5,
>                      ntyp = 3,
>                      ecutwfc = 20 ,
>                     
> /
>  &ELECTRONS
>                conv_thr = 1.0d-8
>                 startingwfc = 'atomic' ,
>                  mixing_mode = 'plain' ,
>                  mixing_beta = 0.7 ,
>                 
> /
> 
> ATOMIC_SPECIES
> Bi 208.9804 Bi.pbe-hgh.UPF
> Te 127.6    Te.pbe-hgh.UPF
> S  32.065   S.pbe-hgh.UPF
> ATOMIC_POSITIONS (angstrom)
>   Bi      0.38788600000000   0.38788600000000   0.38788600000000  
>   Bi      0.61211400000000   0.61211400000000   0.61211400000000 
>   Te      0.77733500000000   0.77733500000000   0.77733500000000 
>   Te      0.22266500000000   0.22266500000000   0.22266500000000 
>   S       0.00000000000000   0.00000000000000   0.00000000000000 
> K_POINTS (automatic)
>  7 7 1 0 0 0   
> and the OUT PUT FILE LOOK LIKE
>