[CP2K-user] [CP2K:19803] Correct band gap for semiconductor slab (with vacuum)

[Martin Konôpka]

Dear Dobromir,

The gap much depends on the functional used. If you used PBE, perhaps try
to use the hybrid functional PBE0. It usually gives wider gaps.
BTW, as far as I know, Kohm-Sham eigenstates with the exception of the
highest occupied one do not have any guaranteed physical meaning. (The
highest occupied level should be equal to the minus of the ionisation
energy in an ideal DFT, at least for molecules). So, to my knowledge,
people try to use such functionals and parametrisations that give them
Kohn-Sham gaps equal (approximately) to experimental optical band gaps. I
my opinion, this is just a pragmatic approach, not an ab initio one.

Best regards
Martin.


st 24. 1. 2024 o 11:33 Dobromir A Kalchevski <dobromirak at gmail.com>
napísal(a):

> Hello,
>
> I was trying to find the band gap of a SiC slab (the surface is cut by the
> {111} orientation) and the result is always wrong (the band gap is way too
> small), due to (as far as my understanding goes) spurious interaction among
> surface states. I know that terminating the surface dangling bonds/free
> electrons with H atoms should help, but I am worried that the H will alter
> the crystal too much. Is there another way to do it ?
>
> Currently the system is 12 Si atoms, 12 C atoms and H-terminated "bottom"
> surface. I am using the periodic Poisson solver in 3D, while leaving enough
> space in the direction perpendicular to the surface.
>
> Best Regards,
> Dobromir
>
>
>
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