Calculating exciton binding energy of α-Al2O3

[Jike.Wang]

Hello,
I am trying to calculate the exciton banding energy of α-Al2O3, but I don't know how to set the HFSCREEN, AEXX and NBSEEIG values in the INCAR file to get the correct rusults. Could you give me some sugesstions on how to set them? Thanks!

[jonathan_lahnsteiner2]

Dear Jike Wang,

It is possible to check our wiki pages for setting the appropriate INCAR values. The wiki page of HFSCREEN mentions that 0.2-0.3 are reasonable values. You can find further information on the wiki page about hybrid functionals. Also for AEXX the wiki mentions default values which can be used. And the tag NBSEEIG controls how many eigenvectors are written to the BSEFATBAND file. So this will not directly effect your calculation but the output. So you have to decide how many eigenvectors you are going to need.

Fine tuning these parameters can be done by doing parameter scans and comparing your results to experiment. Then choosing the set of parameters that fit experiment best. It is also possible to check for other computational studies examining similar materials and then using the parameters presented there. Maybe this paper could be worth a look for your problem https://journals.aps.org/prb/abstract/1 ... 110.075204

All the best Jonathan

[Jike.Wang]

Dear Jonathan,
Thanks for your reply! I have another question and hope for discussing with you. If I have searched the appropriate values of AEXX and HFSCREEN to calculate the exciton banding energy of intact Al2O3, can I use the same values to calculate the Al2O3 with oxygen vacancies?
Best wishes,
Jike Wang

[jonathan_lahnsteiner2]

Dear Jike Wang,

In principle you should be able to use the same set of parameters for treating oxygen vacancies. If you want to be completely sure you can compute the exciton binding energy with the oxygen vacancy and compare to some experimental paper. If the discrepancies between experimental and computed values are too large you could start tuning your parameters. But when comparing computational results with and without oxygen vacancy you should stick to the same set of parameters.

All the best Jonathan