[Pw_forum] Dielectric constant calculations for InAs

[Andrea Dal Corso]

The gap of InAs is not correct with PBE. Your system is probably
metallic. Please check the gap before computing the dielectric constant.

HTH,

Andrea 

On Tue, 2015-09-08 at 17:48 +0800, Zhiping Xu wrote:
> Dear all:
> 
> I am using pw.x and ph.x to calculate the dielectric constant of InAs, and here are some problems with the calculations.
> 
> (1) After structural relaxation using vc-relax, the stress is now zero (confirmed using scf calculations for the final structure). 
> 
>      convergence has been achieved in  10 iterations
> 
>      Forces acting on atoms (Ry/au):
> 
>      atom    1 type  1   force =     0.00000000    0.00000000    0.00000000
>      atom    2 type  2   force =     0.00000000    0.00000000    0.00000000
> 
>      Total force =     0.000000     Total SCF correction =     0.000000
> 
> 
>      entering subroutine stress ...
> 
>           total   stress  (Ry/bohr**3)                   (kbar)     P=    0.00
>    0.00000001  -0.00000000  -0.00000000          0.00     -0.00     -0.00
>   -0.00000000   0.00000001   0.00000000         -0.00      0.00      0.00
>   -0.00000000   0.00000000   0.00000001         -0.00      0.00      0.00
> 
> 
> However, the following phonon calculation predicts not only negative phonon frequency at q = 0, but also very strange dielectric constant.
> 
>           Dielectric constant in cartesian axis 
> 
>           (    -230.720680077      -0.000000000       0.000000000 )
>           (      -0.000000000    -230.720680077       0.000000000 )
>           (       0.000000000       0.000000000    -230.720680077 )
> 
>           Effective charges (d Force / dE) in cartesian axis
> 
>            atom      1   In 
>       Ex  (        9.55076        0.00000        0.00000 )
>       Ey  (        0.00000        9.55076        0.00000 )
>       Ez  (        0.00000        0.00000        9.55076 )
>            atom      2   As 
>       Ex  (       -9.43886        0.00000        0.00000 )
>       Ey  (       -0.00000       -9.43886       -0.00000 )
>       Ez  (        0.00000        0.00000       -9.43886 )
> 
>      Diagonalizing the dynamical matrix
> 
>      q = (    0.000000000   0.000000000   0.000000000 ) 
> 
>  **************************************************************************
>      freq (    1) =      -6.064621 [THz] =    -202.293974 [cm-1]
>      freq (    2) =      -6.064621 [THz] =    -202.293974 [cm-1]
>      freq (    3) =      -6.064621 [THz] =    -202.293974 [cm-1]
>      freq (    4) =       0.164141 [THz] =       5.475159 [cm-1]
>      freq (    5) =       0.164141 [THz] =       5.475159 [cm-1]
>      freq (    6) =       0.164141 [THz] =       5.475159 [cm-1]
>  **************************************************************************
> 
> The input files are attached below for your reference. 
> 
> (2) One more question, the vc-relax calculation converges at zero stress, which was calculated using the cut-off set for initial cell parameters, so one has to redo the calculations using the new cell parameters following the suggestion at http://www.quantum-espresso.org/faq/self-consistency/#6.11 <http://www.quantum-espresso.org/faq/self-consistency/#6.11>. Is there any better (more automatic) way to obtain a final relaxed cell/atom structures?
> 
> Could any one help me on these two questions?
> 
> Thank you,
> 
> Zhiping
> 
> input files:
> 
> —scf.in—
> &control
>   calculation     = 'scf',
>   restart_mode    = 'from_scratch',
>   pseudo_dir      = '/home/xuzp/bin/lib/upf_files',
>   outdir          = '.',
>   prefix          = 'InAs',
>   tstress         = .true.
>   tprnfor         = .true.
>   wf_collect      = .true.
> /
> &system
>   ibrav           = 2, 
>   celldm(1)       = 11.69675,
>   nat             = 2, 
>   ntyp            = 2,
>   ecutwfc         = 90,	
> /
> &electrons
>   diagonalization = 'cg'
>   conv_thr        =  1.0d-10
> /
> 
> ATOMIC_SPECIES
>  In  111.818  In.pbe-dn-rrkjus_psl.0.2.2.UPF
>  As   74.920  As.pbe-n-rrkjus_psl.0.2.UPF
> 
> ATOMIC_POSITIONS crystal
>  In 0.00 0.00 0.00
>  As 0.25 0.25 0.25
> 
> K_POINTS automatic 
>  9 9 9 0 0 0 
> 
> —ph.in—
> phonons of InAs
> &inputph
>   tr2_ph   = 1.0d-16,
>   niter_ph = 100,
>   prefix   = 'InAs',
>   epsil    = .true.		  
>   amass(1) = 111.818,
>   amass(2) = 74.920,
>   outdir   = '.',
>   fildyn   = 'InAs.matdyn',
> /
> 0.0 0.0 0.0
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-- 
Andrea Dal Corso                    Tel. 0039-040-3787428
SISSA, Via Bonomea 265              Fax. 0039-040-3787249
I-34136 Trieste (Italy)             e-mail: dalcorso at sissa.it