[Wien] [SPAM?] How to select the appropriate nband in hybrid functionals calculations

[Yifan Ding]

Dear Wien2k developers，


When YS-PBE0 is used to calculate the DOS of pristine h-BN, the problem I encounter is that I don't know how to select the appropriate nband to obtain the DOS of energy window -20 eV ~ 20 eV.


At first, I calculated the DOS of pristine h-BN using PBE96. The emin and emax in case.in1 file are -9.0 and 2.5, respectively. I can easily get the DOS of -20 eV ~ 20 eV that I need. Then I executed init_hf_lapw, and I set nband in case.inhf file to 14 ( the number of occupied bands plus one) according to the following contents in case.scf


:BAN00001:   1   -1.024214   -0.744172  2.00000000
:BAN00002:   2   -1.013037   -0.743874  2.00000000
:BAN00003:   3   -0.370466   -0.032709  2.00000000
:BAN00004:   4   -0.368369    0.033611  2.00000000
:BAN00005:   5   -0.240838    0.187128  2.00000000
:BAN00006:   6   -0.240784    0.187128  2.00000000
:BAN00007:   7   -0.006555    0.283584  2.00000000
:BAN00008:   8    0.032524    0.287635  2.00000000
:BAN00009:   9    0.598642    0.890756  0.00000000
:BAN00010:  10    0.625260    1.041091  0.00000000
:BAN00011:  11    0.874243    1.203608  0.00000000
:BAN00012:  12    1.014159    1.265192  0.00000000
:BAN00013:  13    1.122810    1.303539  0.00000000
        Energy to separate low and high energystates:   -0.42047


:NOE  : NUMBER OF ELECTRONS          =  16.000


:FER  : F E R M I - ENERGY(TETRAH.M.)=   0.2876346466
:GMA  : POTENTIAL AND CHARGE CUT-OFF  12.00 Ry**.5



Meanwhile, other contents of the case.inhf file are set to YS-PBE0 for calculation. When I executed run_lapw -hf and finished the DOS calculation, I found that the energy window maximum of DOS can only reach 13.42366 eV, but emin and emax in the case.in1 file are still -9.0 and 2.5. I noticed that first three lines of case.dos1ev in PBE96 calculations show:


#  BAND   28          
#EF=   0.00000     NDOS= 3     NENRG= 1750    Gaussian bradening: 0.01600
# ENERGY  total-DOS        1:total        2:total   



Therefore, I changed the nband of case.inhf file in YS-PBE0 calculation to 28, and finally successfully calculated the density of States of -20 eV ~ 20 eV that I needed. Because the structure of h-BN is very simple, when I increase nband from 14 to 28, the increase of calculation time is not particularly obvious.


When I need to calculate the DOS of h-BN with defects, I set 3*3*1 supercell. At this time, nband obtained from case.scf and nband obtained from case.dos1ev are 79 and 910, respectively. I guess that when 79 is used, the complete density of States of -20 eV ~ 20 eV cannot be obtained, and when 910 is used, the calculation time cannot be tolerated. Is there a better solution to this situation?



Any comments would be highly appreciated. Thanks in advance!
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