[Pw_forum] Problem with nscf calc. in elongated supercell

[mohsen modaresi]

Hi Nicki
are you sure about the atomic positions?
sincerely yours
Mohsen Modaresi

On 2/26/10, Nicki Frank Hinsche <nicvok at freenet.de> wrote:
> Hi there,
>
> I got some interesting problem troubling me for some time. I am going
> to calculate huge silicon supercells, therefore I am going step by
> step to larger supercells (lowering the symmetries) to check
> convergencies, before I am going to calculate the heavy perturbed
> system afterwards. I started with the diamond lattice (2 atoms, fcc) -
>  > no problem, perfect DOS and bandstructure. Then I lowered to bct
> (body centered tetragonal) with 4 atoms in the basis -> perfect,
> identical (normalized) DOS and perfect bandstructure. Then I switched
> to the cubic 8 atomic cell -> again everything excellent. Now I just
> doubled the cell in z-direction - so lets say two 8 atomic cells in a
> row -> and suddenly the DOS is awful, has no characteristics - nothing
> like before. The bands are nonsense. Despite the scf calculation went
> quite good (in case of wrong atomic positions for instance it would
> not be like that). I guess I am making a quite big mistake, but wonder
> myself whats wrong - I 've tried different k-meshs, smearings, cut-
> offs and I am quite sure its something systematic what I am doing
> wrong. Any idea? The Input files are attached....
>
> thanks a lot, sorry for the long text
>
> Nicki
>
> SCF INPUT:
>
> /
>   &system
>      ibrav= 0, celldm(1)= 10.266, nat= 16, ntyp= 1,
>      ecutwfc =38.0, !smearing ='m-p', degauss =0.01
>   /
>   &electrons
>      conv_thr =  1.0d-10
>      mixing_beta = 0.25
>   /
> CELL_PARAMETERS {cubic}
> 1.0 0.0 0.0
> 0.0 1.0 0.0
> 0.0 0.0 2.0
> ATOMIC_SPECIES
> Si  28.086  Si.vbc.UPF
> ATOMIC_POSITIONS
> Si 0.00 0.00 0.00
> Si 0.00 0.50 0.25
> Si 0.50 0.00 0.25
> Si 0.50 0.50 0.00
> Si 0.25 0.25 0.125
> Si 0.25 0.75 0.375
> Si 0.75 0.25 0.375
> Si 0.75 0.75 0.125
> Si 0.00 0.00 0.50
> Si 0.00 0.50 0.75
> Si 0.50 0.00 0.75
> Si 0.50 0.50 0.50
> Si 0.25 0.25 0.625
> Si 0.25 0.75 0.875
> Si 0.75 0.25 0.875
> Si 0.75 0.75 0.625
> K_POINTS {automatic}
>    12 12 6 0 0 0
>
>
> NON SCF DOS CALCULATION:
>
>   &system
>      ibrav= 0, celldm(1)= 10.266, nat= 16, ntyp= 1,
>      ecutwfc =38.0,nbnd=40, occupations='tetrahedra'
>   /
>   &electrons
>      conv_thr =  1.0d-10
>      mixing_beta = 0.25
>   /
> CELL_PARAMETERS {cubic}
> 1.0 0.0 0.0
> 0.0 1.0 0.0
> 0.0 0.0 2.0
> ATOMIC_SPECIES
> Si  28.086  Si.vbc.UPF
> ATOMIC_POSITIONS
> Si 0.00 0.00 0.00
> Si 0.00 0.50 0.25
> Si 0.50 0.00 0.25
> Si 0.50 0.50 0.00
> Si 0.25 0.25 0.125
> Si 0.25 0.75 0.375
> Si 0.75 0.25 0.375
> Si 0.75 0.75 0.125
> Si 0.00 0.00 0.50
> Si 0.00 0.50 0.75
> Si 0.50 0.00 0.75
> Si 0.50 0.50 0.50
> Si 0.25 0.25 0.625
> Si 0.25 0.75 0.875
> Si 0.75 0.25 0.875
> Si 0.75 0.75 0.625
> K_POINTS {automatic}
> 12 12 6 0 0 0
>
>
> -------------------------------------------------------------
> Nicki Frank Hinsche, Dipl. Phys.
> Institute of physics - Theoretical physics,
> Martin-Luther-University Halle-Wittenberg,
> Von-Seckendorff-Platz 1, Room 1.07
> D-06120 Halle/Saale, Germany
> Tel.: ++49 345 5525460
> -------------------------------------------------------------
>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum
>