Author Topic: problems with Hgga_hse06 and MGGA calculation to transmission spectrum  (Read 413 times)

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Offline Lim changmin

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Hello, everyone

Recently I got some serious problems with calculating transmission with mgga.

I calculated transmission for Si in 110 direction by following the example on the quantumATK webpage(https://docs.quantumatk.com/tutorials/transmission_gr_mos2/transmission_gr_mos2.html#mos2).

I expected that the transmission should be 0 for the band gap.
However, I got a non-zero transmission for the energy in the band gap as seen in the attached Transmission vs. Energy plot.
I also calculated the band structure which is also attached in this post. And I could see the band structure calculation shows a clear band gap.
I attached the code that I used.

Please take a look and give me any advices to solve this problem.

Thank you

Offline Anders Blom

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A few things to check and comment on here.

First, do you see the same thing with LDA or GGA, i.e. is it specifically a problem of MGGA? If it is, it makes it a bit more interesting to investigate.

However, apart from perhaps a somewhat instructive tutorial example, the calculation doesn't really have any value. The transmission spectrum of any bulk material should really just be counting the states at each energy; in 1D this is trivial and gives you an integer staircase, while in 2D and 3D it's a bit more complex due to k-point sampling, but conceptually still the same. To make an interesting calculation, one should create an extended device with some scattering centers. If also in this case the transmission is non-zero in the band gap, I agree there is a big problem, but we have never seen that.

Now, I am not trying to minimize the potential issue, we should probably look into it, but it's also not a serious problem if this is isolated to the bulk transmission, as that is generally not something you need to compute; we support it mainly for legacy reasons. Or, to some extent for educational purposes, so again, it should of course calculate it correctly. Thus, if you can check it with LDA also, it will help us a bit.

Offline Lim changmin

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Sorry for the late reply.
Actually I finally solved the problem
The problem was that I didn't used geometry optimization during calculation.
Because other analysis, such as bandstructure and fermi surface etc. was shown without an error, I assumed that transmission spectrum was the only error that I got.
However, when I done geometry optimization, transmission spectrum showed good results.
sorry for the confusion.