First of all: Setting nband to n_occupied + 1 works tecnically, but
the results will NOT be converged.
This was discussed numerous times. In principle nband should be tested,
until eg. the gap is converged. Typically you need 10-50% more bands
than n_occupied.
Second: You get the DOS only for the bands you calculate. with a certain
nband you get the DOS up to the minimum of the last calculated band
range of the nband' band.If youdon't calculate high energy states, you
cant get a DOS. The emin/emax in case.in1 are for lapw1, but not for hf.
You noticed correctly, that the cpu time scales crucially with nband.
You did not mention anything about the k-mesh.
a) The 3x3 supercell should be done by a 3x3 smaller k-mesh !
b) We have the option of a reduced k-mesh for the hf-potential. This
saves a lot of time and can still be reasonably accurate. Test on the
small system what reduction still gives you converged results.
Am 08.05.2021 um 22:01 schrieb 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:?0?2 ?0?21?0?2 ?0?2-1.024214?0?2 ?0?2-0.744172?0?2 2.00000000/
/:BAN00002:?0?2 ?0?22?0?2 ?0?2-1.013037?0?2 ?0?2-0.743874?0?2 2.00000000/
/:BAN00003:?0?2 ?0?23?0?2 ?0?2-0.370466?0?2 ?0?2-0.032709?0?2 2.00000000/
/:BAN00004:?0?2 ?0?24?0?2 ?0?2-0.368369?0?2 ?0?2 0.033611?0?2 2.00000000/
/:BAN00005:?0?2 ?0?25?0?2 ?0?2-0.240838?0?2 ?0?2 0.187128?0?2 2.00000000/
/:BAN00006:?0?2 ?0?26?0?2 ?0?2-0.240784?0?2 ?0?2 0.187128?0?2 2.00000000/
/:BAN00007:?0?2 ?0?27?0?2 ?0?2-0.006555?0?2 ?0?2 0.283584?0?2 2.00000000/
/:BAN00008:?0?2 ?0?28?0?2 ?0?2 0.032524?0?2 ?0?2 0.287635?0?2 2.00000000/
/:BAN00009:?0?2 ?0?29?0?2 ?0?2 0.598642?0?2 ?0?2 0.890756?0?2 0.00000000/
/:BAN00010:?0?2 10?0?2 ?0?2 0.625260?0?2 ?0?2 1.041091?0?2 0.00000000/
/:BAN00011:?0?2 11?0?2 ?0?2 0.874243?0?2 ?0?2 1.203608?0?2 0.00000000/
/:BAN00012:?0?2 12?0?2 ?0?2 1.014159?0?2 ?0?2 1.265192?0?2 0.00000000/
/:BAN00013:?0?2 13?0?2 ?0?2 1.122810?0?2 ?0?2 1.303539?0?2 0.00000000/
/?0?2 ?0?2 ?0?2 ?0?2 Energy to separate low and high energystates:?0?2
?0?2-0.42047/
/
/
/:NOE?0?2 : NUMBER OF ELECTRONS?0?2 ?0?2 ?0?2 ?0?2 ?0?2 =?0?2 16.000/
/
/
/:FER?0?2 : F E R M I - ENERGY(TETRAH.M.)=?0?2 ?0?20.2876346466/
/:GMA?0?2 : POTENTIAL AND CHARGE CUT-OFF?0?2 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?0?2of 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:
/#?0?2 BAND?0?2 ?0?228 /
/#EF=?0?2 ?0?20.00000?0?2 ?0?2 ?0?2NDOS= 3?0?2 ?0?2 ?0?2NENRG= 1750?0?2 ?0?2
Gaussian bradening: 0.01600/
/# ENERGY?0?2 total-DOS?0?2 ?0?2 ?0?2 ?0?2 1:total?0?2 ?0?2 ?0?2 ?0?2 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.?0?2At 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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