[Wien] Deformation Potential

[Laurence Marks]

You need to explore a bit more exactly what is being output by the various
codes, and how potentials are treated in W2k and other DFT codes. Key
points:

1. For a charge neutral cell one can add or subtract a constant potential
without changing the energy. It is standard in dft to subtract the mean
potential to avoid singularities. Thus all the energies etc in W2k are
referenced to this.

2. When you do a band structure plot/analysis the code may reference
everything to the Fermi energy. The reason your VBE was always zero is
(with tetra) that the VBE is E_f. You can change the referencing to
absolute values via options, or use your current values but correct for the
value of E_f from case.scf2.

3. There is a variation on the mean with strain, see the paper I
referenced. Getting this is not simple. One approximate method is the Ibers
approximation that we mention. To be more accurate you need to setup a
large surface slab where the vacuum references to zero. You then apply
strain to this and calculate the variation of something like a core energy
at the center of the slab with strain.

N.B., if anyone has a method that will find the absolute value mire simply
I am interested.

___
Emeritus Professor Laurence Marks (Laurie)
Department of Materials Science and Engineering, Northwestern University
www.numis.northwestern.edu
"Research is to see what everybody else has seen, and to think what nobody
else has thought" Albert Szent-Györgyi

On Mon, Feb 9, 2026, 04:34 uchit chaudhary <uchitchaudhary99 at gmail.com>
wrote:

> Dear experts,
> My aim to calculate the deformation potential is for relaxation time
> measurement. For this I applied the strain method and noted the band edge
> energy value for VBM and CBM from the band structure. I found that VBM is
> exactly at Fermi energy at 0 and there is no any change with strain. So, I
> could not find the band energy edge of the VBM, which is essential in
> relaxation time calculation. I checked the calculation of this paper: [8]
> https://doi.org/10.1038/srep22778
> I found that the band structure VBM lies exactly at 0, but the paper has
> reported differently; that may be for measuring deformation potential. The
> paper has mentioned this :   Figure 2(a) presents the band edge energy (E
> edge ) values at the CBM and VBM for electrons and holes as a function of
> the uniaxial strain δ β assigned along the a-axis, respectively, exhibiting
> good linear dependence. Here, the average electrostatic potential 32 is set
> as a reference to obtain the absolute band edge shifts. The DP constant λ β
> values, as listed in Table 1, are similar for electrons (λ β = − 15.94 eV)
> and holes (λβ  = − −14.51 eV). Now, my question is how to do this
> calculation for measuring band edge energy for VBM and CBM accurately?
>
> On Sun, Feb 8, 2026 at 5:53 PM uchit chaudhary <uchitchaudhary99 at gmail.com>
> wrote:
>
>> Dear experts,
>>
>> How to calculate the deformation potential in Wien2k?
>>
>>
>>
>>
>> Best Regards,
>> Wien2k user
>> uchit
>>
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