GW+BSE Calculations

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GW+BSE Calculations

Postby dscullion12 » Mon May 15, 2017 10:09 am

Dear VASP Users,

I have been carrying out GW+BSE calculations on a semi-conducting material. When carrying out the BSE calculation I use the WAVECAR and WAVEDER files from the groundstate calculation and the WFULLxxxx.tmp files from the GW calculation. However, the GW calculations has increased the energy of the top of the valence band such that it is now larger than the fermi level of the groundstate calculation.

When carrying out the BSE calculation the material is being treated, wrongly, as a metal.

Would anyone have a solution to this problem?

Kind regards,

Declan
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Re: GW+BSE Calculations

Postby gbal » Thu May 18, 2017 10:22 am

Hi there,
First i would say that this would fit better for "physics questions" than "bug reports", but here we are.

Any special reason to use LDA/GGA WAVECAR and WAVEDER?

I normally calculate BSE using the outputs from the GW calculation.

Maybe you wanna make TDDFT (just don't have the GW files there) if you need to keep using the ground-state files.
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Re: GW+BSE Calculations

Postby dscullion12 » Fri May 19, 2017 12:10 pm

Thank you for the quick reply.

I can see reasons for using the GW WAVECAR files instead of the groundstate when solving the BSE. Thank you for clearing this up.

I would have one more question though. Depending on the parallelisation method I use (KPAR or a combination of NPAR and NCORE) I get different results from my G0W0 calculations. For example, using KPAR = 2, NPAR = default, NCORE = default I obtain a bandgap of 3.19 eV. If, however, I used KPAR = default and NPAR = 8, NPAR = 96 I obtain a bandgap of 5.23 eV.

Nothing has been changed between the two calculations apart from the method of parallelisation.

Any help would be greatly appreciated.

Kind Regards,

Declan
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Re: GW+BSE Calculations

Postby gbal » Mon May 29, 2017 10:16 am

dscullion12 wrote:Nothing has been changed between the two calculations apart from the method of parallelisation.


Are you sure about this?

When you change parallelization tags, you change several things, including number of bands and readability of files depending on it.
My first bet would be that you are with different settings. And even in the case that you are reading the files properly, this is already a different setup that will influence the results. GW parallelization works in a different manner than standard DFT or HSE, prepare the calculation accordingly.
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