[CP2K-user] [CP2K:19807] Correct band gap for semiconductor slab (with vacuum)

[Dobromir A Kalchevski]

Dear Martin,

Thank you for the answer. 

Unfortunatelly, methods like PBE0 and HSE06 are too expensive for the 
machine I have.

Best Regards,
Dobromir

  

On Wednesday, January 24, 2024 at 12:56:00 PM UTC+2 Martin Konôpka wrote:

> 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 <dobro... 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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>>
>

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