[Pw_forum] About zero forces.

[Giovanni Cantele]

Hi,

very likely this is related with the symmetry of your starting configuration.

By default, QE uses symmetry. All forces which must be zero by symmetry, are NOT computed but SET to zero.
This is helpful because saves computing time, but can induce errors if the starting configuration as a higher
symmetry than “required”. 

If you are not sure that the symmetry of your starting configuration is too high, you can try to break it by moving
one or more atoms in the unit cell, by a small quantity.

Giovanni



On 02 Apr 2014, at 11:38, Mutlu COLAKOGULLARI <mutlusan at yahoo.com> 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
> ______________________________________________________________________
> <CoPt_tP4.out>_______________________________________________
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> http://pwscf.org/mailman/listinfo/pw_forum

-- 

Giovanni Cantele, PhD
CNR-SPIN
c/o Dipartimento di Fisica
Universita' di Napoli "Federico II"
Complesso Universitario M. S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy
e-mail: giovanni.cantele at spin.cnr.it
Phone: +39 081 676910
Skype contact: giocan74

ResearcherID: http://www.researcherid.com/rid/A-1951-2009
Web page: http://people.na.infn.it/~cantele

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