[Pw_forum] About zero forces.

[Ari P Seitsonen]

Dear Mutlu,

   There are no degrees of freedom to relax, the system has such high a 
symmetry (P4/mm'm'?) that by that symmetry all the forces are zero. You 
have to break the symmetry by shifting the atoms if you want non-zero 
forces. If you want to relax the lattice vectors, please use

       calculation = 'vc-relax'

   Why do you assume that the forces should be non-zero?

     Greetings,

        apsi

-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-
   Ari Paavo 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 Wed, 2 Apr 2014, Mutlu COLAKOGULLARI wrote:

> Hello People,
> 
> I want to relax CoPt bulk material. It has face-centered tetragonal (tP4)
> structural type. The relaxation is always finisihing after 1 scf cycle and 0
> bfgs step. The forces are always zero. I mean the system is not relaxing. I
> googled the problem and I tried something in input, nevertheless I failed
> for every try. What am I doing something wrong? Do you have any suggestion
> or comment or web page? 
> I am using svn version with latest updates.
> Here is my input file: 
> 
>  &control
>     calculation   = 'relax',
>     restart_mode  = 'from_scratch',
>     pseudo_dir    = '/home/mutlusan/Desktop/CoPt/pseudos',
>     outdir        = '/home/mutlusan/Desktop/CoPt/outdir.CoPt',
>     prefix        = 'CoPt',
>     tprnfor       = .true.
>     tstress       = .true.
>      wf_collect    = .true.
> !    etot_conv_thr = 1.0D-12,
> !    forc_conv_thr = 1.0D-11 ,
>             nstep = 300  ,
>            disk_io = 'low'
>  /
>  &system
>            ibrav = 6,
>      celldm(1)= 7.182849031 !a=3.801 A
>      celldm(3)= 0.979479084  !c=3.723 A 
>             ntyp = 2,
>               nat = 4,
>           ecutwfc = 85,
>           ecutrho = 850,
>       occupations = 'smearing'
>          smearing = 'mv'
>           degauss = 0.01
>  nspin=2
>  starting_magnetization(1)=0.5
>  /
>  &electrons
>     conv_thr         = 1.0d-8,
>     diagonalization  = 'david'
>     diago_david_ndim = 8
>     mixing_mode      = 'plain'
>     mixing_beta      = 0.7
>     mixing_ndim       = 8
>  /
> 
>  &ions
> !   upscale=100,
>   ion_dynamics      = "bfgs",
>           bfgs_ndim = 8
> /
> !CELL_PARAMETERS 
> !  7.182849031   0.000000   0.000000   
> !  0.000000   7.182849031   0.000000   
> !  0.000000   0.000000   7.0355450393 
> ATOMIC_SPECIES
>   Co    58.9332  Co.pbe-sp-van.UPF 
>   Pt   195.0800  Pt.pbe-n-van.UPF
> ATOMIC_POSITIONS (crystal)
> Co         0.00000        0.00000        0.00000
> Co         0.50000        0.50000        0.00000
> Pt         0.50000        0.00000        0.50000
> Pt         0.00000        0.50000        0.50000
>   K_POINTS automatic
> 8 8 8 1 1 1
> 
> I have attached the output file. 
> 
> with my best wishes,
> 
>      Mutlu. 
> ______________________________________________________________________
> Mutlu COLAKOGULLARI
> Phone     : +90 (284) 235 1179 (ext: 1207)
> Address  :  Trakya University
>                Sciences Faculty,  Department of Physics,
>                Balkan Campus, (22100) Merkez - Edirne - TURKEY
> Home page: http://goo.gl/DNXfNC
> ______________________________________________________________________
> 
>