QuantumATK Forum

QuantumATK => General Questions and Answers => Topic started by: lknife on June 18, 2017, 05:17

Title: why are the band structures calculated by GGA and SOGGA totally different?
Post by: lknife on June 18, 2017, 05:17: I can understand some minors difference between the results calculated by GGA and SOGGA.

However, seen attached pictures, for calculations with the same bulk configuration and all other identical parameters, the band structures calculated by GGA and SOGGA are totally different. I don't know which one should be more reasonable, since there is no reference for this new bulk configuration. Can anyone here help me with this problem?

Thank you very much for you time and kind help!
Title: Re: why are the band structures calculated by GGA and SOGGA totally different?
Post by: Petr Khomyakov on June 19, 2017, 09:00: It is hard to say anything about it without seeing the actual scripts.
Title: Re: why are the band structures calculated by GGA and SOGGA totally different?
Post by: lknife on June 19, 2017, 17:45: Please see the attached .py files for the calculation. One is for GGA calculation and the other is for SOGGA calculation. For the SOGGA calculation, I just modified the script by changing the GGA method to SOGGA method.
Title: Re: why are the band structures calculated by GGA and SOGGA totally different?
Post by: Anders Blom on June 19, 2017, 20:59: Does the SOGGA calculation converge?
Title: Re: why are the band structures calculated by GGA and SOGGA totally different?
Post by: lknife on June 20, 2017, 02:05: Thank you very much for you reply. You are quite right, the SOGGA calculation did not converge. That must be the reason! Because the .log for the SOGGA calculation is quite large, I cannot post it here.

Then what can I do? To increase the iteration step to a larger number or do something else? Could you please give me your valuable advises to it?

Thank you again for your kind help! You are really helpful!
Title: Re: why are the band structures calculated by GGA and SOGGA totally different?
Post by: Anders Blom on June 20, 2017, 02:18: Sometimes it works to simply use the GGA or equivalent spin-polarized converged result as starting guess for SOGGA.
Otherwise usual "tricks" apply: lower mixing, fewer history steps, more k-points, etc can be useful strategies.
Title: Re: why are the band structures calculated by GGA and SOGGA totally different?
Post by: lknife on June 20, 2017, 21:55: Thank you very much for your valuable advises!