[Wien] The value of band gap from band structure is more less than DOS?

[Rocquefelte]

Dear Tayebeh,

This difference between the "DOS" gap and the "band structure" gap is 
simply related to the nature of the bands which define your gap. Indeed, 
these bands are significantly dispersed (which means few states at the 
top of the valence band and at the bottom of the conduction band). As a 
consequence, it leads to a slow increase of the DOS (few states) and the 
DOS starts to be significant only at higher energy values, which means 
that the apparent gap is larger than the fundamental gap obtained from 
the band structure.
Similar question arise when asking the difference between fundamental 
gap and optical gap. In the optical gap the notion of efficiency enter 
in terms of transition probability but also in terms of number of 
states, if the band structure is strongly dispersed and also if the 
transition is allowed, the optical gap will be larger than the 
fundamental gap.

Hope that this will help you

Regards

Xavier


taiiebeh molarooy a écrit :
> Dear wien users,
> Hi, I have calculated electronic structure of CNT, but there is any 
> problem with value of band gap.
> The value of band gap from band structure is less than DOS. For 
> example bad gap of CNT(10-0) from band structure is calculated about 
> 0.35 eV while it is 0.9 eV from DOS. And also for CNT(16-0) with 64 
> atom, it is about 0.5 eV while it is 1.2 eV from DOS. 
> Do you know why the value of band gap is different?
>  
> Another problem is that we are expected that value of band gap must be 
> decreased by increasing diameter of CNT, while my results is inverse!
> Do you know why are these problems?
>  
> Thank you very much in advance.
> Yours sincerely,
> Tayebeh.
>
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