[Pw_forum] the sum of the born effective charge in phonon calculation

[Eyvaz Isaev]

Dear Cheng,

>     conv_thr = 1.D-12,
You wast time with this threshold. Use less strong criteria.

>           -2.01782      
>            2.04775       

I would say the Born charges are equivalent (by absolut values) with a numerical noise. Within this noise charges' sum is zero.

>   tr2_ph=1.0d-12,
Try d-14, and more ecutwfc.

Bests,
Eyvaz.

-------------------------------------------------------------------
Prof. Eyvaz Isaev, 
Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia, 
Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden 
Condensed Matter Theory Group, Uppsala University, Sweden 
Eyvaz.Isaev at fysik.uu.se, isaev at ifm.liu.se, eyvaz_isaev at yahoo.com


--- On Mon, 6/29/09, 程迎春 <yccheng.nju at gmail.com> wrote:

> From: 程迎春 <yccheng.nju at gmail.com>
> Subject: [Pw_forum] the sum of the born effective charge in phonon calculation
> To: "PWSCF Forum" <pw_forum at pwscf.org>
> Date: Monday, June 29, 2009, 7:10 PM
> Dear pwscf users,
>     I calculated the phonon of ZnS at Gamma
> point.  I checked the output file, and found that the sum
> of the born effective charge is not zero.
> ================================
>           Effective charges E-U in cartesian
> axis
>            atom     1
>           (       -2.01782       
> 0.00000        0.00000 )
>           (        0.00000      
> -2.01782        0.00000 )
>           (        0.00000       
> 0.00000       -2.01782 )
>            atom     2
> 
>           (        2.04775       
> 0.00000        0.00000 )
>           (        0.00000       
> 2.04775        0.00000 )
>           (        0.00000       
> 0.00000        2.04775 )
> ================================
> 
> My question :
> 1. why the sum of the effectvie charge is not
> zero?
> 2.how to improve the calculation of born effective
> charge?
>  
> The following is my input files:
> scf.in
>  &CONTROL
>                        title = fine,
>                       prefix =
> 'zns'
>                  calculation =
> 'scf' ,
>                 restart_mode =
> 'from_scratch' ,
>                   wf_collect = .false. ,
> 
>                       outdir =
> './' ,
>                   pseudo_dir =
> './' ,
>                      tstress = .true.
> ,
>                      tprnfor = .true.
> ,
>                        nstep = 100 ,
> 
>  /
>  &SYSTEM
>                        ibrav = 2,
>                    celldm(1) =
> 10.204964632,
>                          nat = 2,
>                         ntyp = 2,
>                      ecutwfc = 80,
>                        nosym =
> .false. ,
> 
>  /
>  &ELECTRONS
>             electron_maxstep = 100,
>                     conv_thr = 1.D-12,
>  /
> ATOMIC_SPECIES
>     S   32.066   16-S.GGA.fhi.UPF
>     Zn  65.409   30-Zn.GGA.fhi.UPF
> ATOMIC_POSITIONS crystal
> 
> S        0.250000000   0.250000000  
> 0.250000000
> Zn       0.000000000   0.000000000   0.000000000
> K_POINTS automatic
>   16 16 16 0 0 0
> 
> ph.in
> phonon calculation for ZnS
> &inputph
>   tr2_ph=1.0d-12,
>   prefix='zns',
>   epsil=.true.,
>   trans=.true.,
>   lraman=.true.,
>   elop=.true.,
>   amass(1)=32.066,
>   amass(2)=65.409,
>   outdir='./',
> 
>   fildyn='ZnS_IR.dynG',
>   fildrho='ZnS_IR.drho',
>  /
> 0.0 0.0 0.0
> 
> 
> -- 
> Y. C. Cheng
> Department of Physics
> Nanjing University
> Nanjing 210093
> P. R. China
> Tel: 86-25-83592907
> Email: yccheng.nju at gmail.com
> 
> 
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> 
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