[Pw_forum] PHonon underestimates the dielectric tensor

[Ari P Seitsonen]

Dear Mohamed,

   This probably does not resolve your problem, but still: Did you check 
the convergence of the properties with respect to the cut-off energy, 
'ecutwfc'? We traditionally used values of 80-100 Ry, but I must confess 
that I do not know exactly this potential. Also I would converge the 
final electronic structure a bit better than the default value of 10^-6 
('conv_thr'). Are these relaxed atomic positions?

     Greetings,

        apsi

-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-
   Ari Paavo Seitsonen / Ari.P.Seitsonen at iki.fi / http://www.iki.fi/~apsi/
   Ecole Normale Supérieure (ENS), Département de Chimie, Paris
   Mobile (F) : +33 789 37 24 25    (CH) : +41 79 71 90 935


On Sun, 6 Dec 2015, Mohamed Elshazly wrote:

> 
> Hello everyone,
> 
> 
> I'm trying to reproduce the dielectric constant of alpha-alumina using
> PHonon. However, I'm getting values close to third of the actual dielectric
> constant and cannot figure out why. I also had the same issue with
> Columbite-(Mg), so it's not a particular problem with that material system.
> 
> 
> Here are my SCF and PH input files: 
> 
> 
> &control
> calculation='scf',
> outdir='./out',
> prefix='alo',
> pseudo_dir='.',
> tstress=.true.,
> tprnfor=.true.,
> forc_conv_thr=1.0D-8,
> etot_conv_thr=1.0D-6,
> /
> 
> &system
> ibrav=0,
> celldm(1)=9.69051561,
> nat=10,
> ntyp=2,
> ecutwfc=50,
> /
> 
> &electrons
> diago_full_acc=.true.,
> /
> 
> &ions
> /
> 
> ATOMIC_SPECIES
> O 15.9994 O.pbe-mt.UPF
> Al 26.981539 Al.pbe-mt_fhi
> 
> CELL_PARAMETERS alat
>    0.444822702  -0.256818507   0.805845773
>   -0.000000000   0.513637014   0.805845773
>   -0.444822702  -0.256818507   0.805845773
> 
> ATOMIC_POSITIONS crystal
> O        0.058814216   0.749985721   0.441239527
> O        0.250014279   0.558760473   0.941185784
> O        0.441239527   0.058814216   0.749985721
> O        0.558760473   0.941185784   0.250014279
> O        0.749985721   0.441239527   0.058814216
> O        0.941185784   0.250014279   0.558760473
> Al       0.148217545   0.148217545   0.148217545
> Al       0.351772827   0.351772827   0.351772827
> Al       0.648227173   0.648227173   0.648227173
> Al       0.851782455   0.851782455   0.851782455
> 
> K_POINTS automatic
> 16 16 16 0 0 0
> 
> PH:
> 
> alo_dielectric
> 
> &INPUTPH
> tr2_ph=1e-15,
> outdir='./out',
> prefix='alo',
> epsil=.true.,
> /
> 
> 0 0 0
> 
> Any help would be greatly appreciated.
> 
> Mohamed Elshazly
> Edward S. Rogers Department of Electrical and Computer Engineering
> University of Toronto
>