<div>Dear pwscf users,</div>
<div>    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.</div>
<div>================================</div>
<div>          Effective charges E-U in cartesian axis</div>
<div>           atom     1<br>          (       -2.01782        0.00000        0.00000 )<br>          (        0.00000       -2.01782        0.00000 )<br>          (        0.00000        0.00000       -2.01782 )<br>           atom     2<br>
          (        2.04775        0.00000        0.00000 )<br>          (        0.00000        2.04775        0.00000 )<br>          (        0.00000        0.00000        2.04775 )<br>================================</div>

<div>My question :</div>
<div>1. why the sum of the effectvie charge is not zero?</div>
<div>2.how to improve the calculation of born effective charge?</div>
<div> </div>
<div>The following is my input files:</div>
<div><a href="http://scf.in">scf.in</a></div>
<div> &CONTROL<br>                       title = fine,<br>                      prefix = 'zns'<br>                 calculation = 'scf' ,<br>                restart_mode = 'from_scratch' ,<br>                  wf_collect = .false. ,<br>
                      outdir = './' ,<br>                  pseudo_dir = './' ,<br>                     tstress = .true. ,<br>                     tprnfor = .true. ,<br>                       nstep = 100 ,<br>
 /<br> &SYSTEM<br>                       ibrav = 2,<br>                   celldm(1) = 10.204964632,<br>                         nat = 2,<br>                        ntyp = 2,<br>                     ecutwfc = 80,<br>                       nosym = .false. ,<br>
 /<br> &ELECTRONS<br>            electron_maxstep = 100,<br>                    conv_thr = 1.D-12,<br> /<br>ATOMIC_SPECIES<br>    S   32.066   16-S.GGA.fhi.UPF<br>    Zn  65.409   30-Zn.GGA.fhi.UPF<br>ATOMIC_POSITIONS crystal<br>
S        0.250000000   0.250000000   0.250000000<br>Zn       0.000000000   0.000000000   0.000000000<br>K_POINTS automatic<br>  16 16 16 0 0 0<br><br clear="all"><a href="http://ph.in">ph.in</a></div>
<div>phonon calculation for ZnS<br>&inputph<br>  tr2_ph=1.0d-12,<br>  prefix='zns',<br>  epsil=.true.,<br>  trans=.true.,<br>  lraman=.true.,<br>  elop=.true.,<br>  amass(1)=32.066,<br>  amass(2)=65.409,<br>  outdir='./',<br>
  fildyn='ZnS_IR.dynG',<br>  fildrho='ZnS_IR.drho',<br> /<br>0.0 0.0 0.0<br></div>
<div></div><br>-- <br>Y. C. Cheng<br>Department of Physics<br>Nanjing University<br>Nanjing 210093<br>P. R. China<br>Tel: 86-25-83592907<br>Email: <a href="mailto:yccheng.nju@gmail.com">yccheng.nju@gmail.com</a><br>