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

[Vahid Askarpour]

The LDA gap here is around 80meV. The experimental gap is around 150meV.

I may have to manually change the dielectric constant to experimental value before feeding it to EPW.

Thanks Paolo,
Vahid

> On Dec 23, 2025, at 8:09 AM, Paolo Giannozzi <paolo.giannozzi at uniud.it> wrote:
> 
> CAUTION: The Sender of this email is not from within Dalhousie.
> 
> 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
>