[Wien] Band gap calculation

[Gavin Abo]

I don't recall seeing "test_conv-5.0.tar.gz" before.  I'm guessing that 
is the newer version of the full convergence tests package at [1] 
(unsupported at least by this group), which seems to not be accessible 
to the public (and likely only accessible to and perhaps supported by 
the private group [2]).

I'm guessing the algorithm that gets the gap value from the valence band 
maximum (VBM) and conduction band minimum (CBM) is not accurate for your 
calculation case.  Therefore, I would most likely go with the gap that 
you get yourself from the raw data (case.spaghetti_ene [3] or [4]) of 
the band structure plot from spaghetti.

If the differences are small like in [5], a percent difference [6] of 
about 2% [= (1.54 eV - 1.51 eV)/{(1.54 eV + 1.51 eV)/2}*100%] seems 
acceptable.  I believe greater than about 5% in when you should be 
concerned [7].

[1] 
http://wien2k-algerien1970.blogspot.com/2016/09/the-full-version-of-conversgence-tests.html
[2] https://www.facebook.com/groups/wien2k.Algeria/
[3] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg15255.html
[4] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg15258.html
[5] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg19405.html
[6] 
https://www.webassign.net/question_assets/ncsucalcphysmechl3/percent_error/manual.html
[7] https://socratic.org/questions/what-percent-error-is-too-high

On 12/22/2019 11:36 PM, Peeyush kumar kamlesh wrote:
> Dear Gavin Sir,
> Thank you for your response.
> I did k-point convergence test by a test package 
> "test_conv-5.0.tar.gz". I dont know whether it is gives completely 
> satisfactory results or not. If you have any other package for kpt 
> convergence kindly let me know, so that i can do the right 
> calculations. Also I used non shifted k-mash in the calculations of 
> the band gap.
>
> Thank you so much!
> Regards
> Peeyush Kamlesh