[Pw_forum] PHonon underestimates the dielectric tensor

[Mohamed Elshazly]

Hello Apsi,

Thank you for your feedback.

Yes, these are relaxed atomic positions. The values I got for energy and the equilibrium lattice constant were very good, and that's why I went ahead with the phonon calculation. I'm using a Martins-Troullier norm-conserving pseudopotential with a PBE XC functional.

The problem is that I also tried LDA on this material system and PBE on a different material system, same problem. I'm running version 5.2.1 and the examples worked just fine, so it doesn't seem like a bug either. 

I will, however, try better convergence thresholds and update the thread if it fixes the problem. Thank you!

________________________________________
From: pw_forum-bounces at pwscf.org <pw_forum-bounces at pwscf.org> on behalf of Ari P Seitsonen <Ari.P.Seitsonen at iki.fi>
Sent: December-06-15 11:50 AM
To: PWSCF Forum
Subject: Re: [Pw_forum] PHonon underestimates the dielectric tensor

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
>