[Pw_forum] Temperature effect on band gap

[Lorenzo Paulatto]

On Thursday, September 24, 2015 11:28:00 AM reza vatan wrote:
> Dear Lorenzo,
> 
> Thanks for your comment. I tried changing the lattice constants effect band
> gap, but I got reverse trend which was increasing the band gap by
> increasing lattice constants. In experiment, people measure smaller band
> gap in higher temperature (larger lattice constant). By any chance, do you
> know where the problem is?

Well, I don't know. If you have internal degrees of freedom you may have to do 
a relax at each volume..

What I can say is that the band gap in DFT is in no way reliable, there is not 
theoretical reason for it to be correct. If you want an accurate band gap you 
will have to use some beyond DFT method, I think GW or TDDFT, but to be honest 
I know almost nothing about these methods

-- 
Dr. Lorenzo Paulatto
IdR @ IMPMC -- CNRS & Université Paris 6
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