[QE-users] Silicon gap vs. temperature

[Md. Jahid Hasan Sagor]

Have you considered the lattice vibration (phonon) contribution? You need
different atomic positions at different temperatures to include the
phononic effect.

Best
M J Hasan
Mechanical Engineering
University of Maine

On Tue, Aug 13, 2024 at 8:17 AM David Fernandes Machado <dfernandes at laas.fr>
wrote:

> Hello all,
>
>
>
> I am trying to determine the dependence of the energy gap of silicon as a
> function of temperature. In the literature, it is stated that the decrease
> in the energy gap of silicon with increasing temperature can be explained
> by thermal expansion and electron-phonon interaction.
>
>
>
> First, I used the *thermo_pw* library (which uses the QHA approximation)
> to determine the lattice parameter of silicon as a function of temperature.
> Then, I ran the following calculations: SCF, NSCF, DOS, band, and finally
> plotband. I performed these calculations using the lattice parameters of Si
> corresponding to temperatures in a range from 4K to 800K. For this
> simulation, I am using PBE pseudopotentials, an ecutwfc of 25 Ry, and a
> unit cell with 2 atoms.
>
>
>
> The problem is that the gap increases with temperature instead of
> decreasing. I obtained a gap of 0.6187 eV at 4K and 0.6315 eV at 800K.
>
>
>
> I also tried calculating the band structure considering electron-phonon
> coupling using the EPW library, but the gap still increases with
> temperature.
>
>
>
> Has anyone already tried to calculate the silicon gap as a function of
> temperature? What am I doing wrong?
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