[QE-users] Dielectric constant of Bi2Te3 from ph.x seems too large

[Paolo Giannozzi]

Maybe your computed gap is very small (and smaller than the experimental 
one)?

Paolo

On 12/23/2025 1:03 PM, Vahid Askarpour wrote:
> Dear QE Community,
> 
> When doing ph.x calculation on the bulk Bi2Te3 with qe-7.3.1, I get the following for the dielectric constant
> 
>       
> End of electric fields calculation
> Dielectric constant in cartesian axis
> 
> (     492.092803103       0.000000000      -0.000000000 )
> (       0.000000000     492.092803103      -0.000000000 )
> (       0.000000000      -0.000000000     100.437749350 )
> 
> The preliminary scf calculation was done with the following scf.in
> 
> &control
>      calculation='scf',
>      restart_mode='from_scratch',
>      prefix='Bi2Te3',
>      pseudo_dir='./'
>      verbosity='high',
>      tprnfor=.true.,
>      tstress=.true.,
>      etot_conv_thr=1.0d-6
>      forc_conv_thr=1.0d-5
> /
> &system
>      ibrav=0,
>      nat=5, ntyp= 2,
>      ecutwfc = 110,
>      occupations='fixed'
>      lspinorb= .true.
>      noncolin=.true.
> /
> &electrons
>      diagonalization='cg'
>      conv_thr = 1.0e-10
>      mixing_beta = 0.5
>      electron_maxstep = 500
>      mixing_mode = 'plain'
> /
> ATOMIC_SPECIES
> Bi 208.9804  Bi-d_r.upf
> Te 127.6     Te-d_r.upf
> CELL_PARAMETERS (angstrom)
>       2.19309263036978    -1.26618262050178   10.15655859709168
>       0.00000000000000     2.53236524100356   10.15655859709168
>      -2.19309263036978    -1.26618262050178   10.15655859709168
> ATOMIC_POSITIONS (crystal)
> Bi   0.40035000000000   0.40035000000000   0.40035000000000
> Bi   0.59965000000000   0.59965000000000   0.59965000000000
> Te   0.20882000000000   0.20882000000000   0.20882000000000
> Te   0.79118000000000   0.79118000000000   0.79118000000000
> Te   0.00000000000000   0.00000000000000   0.00000000000000
> 
> K_POINTS (automatic)
> 12 12 12 0 0 0
> 
> I expected dielectric constants around 50. I am not sure if I am making a mistake or if this is a bug. Any suggestion is appreciated.
> 
> Thanks,
> 
> Vahid
> 
> Vahid Askarpour
> Department of Physics and Atmospheric Science
> Dalhousie University
> Halifax, Canada
> 
> 
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-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 206, 33100 Udine Italy, +39-0432-558216