[Pw_forum] How to get the usual ~2.4 eV band gap of ZnO with HSE06?

[Tan Hengxin]

Dear Prasenjit,

Thanks for your reply! As you suggested, I can adjust the percentage of EXX
or plus Hubbard U. However, in the literatures for wurtzitw ZnO, when the
EXX is 25% without any other corrections, then the HSE band gap is ~2.4 eV,
which not my case (~2.1 eV). I just don't know why.  I have also done test
with VASP, which gives the gap of ~2.5 eV. Maybe different ab-initio code
would give different results. But I think the difference 0.4 eV is a little
too large.
So my question is, if the PBE pseudopotentials (pps) are good, then why
such pps-based HSE calculation gives a gap with so large difference from
the literatures or VASP? Could you please give me any suggestions on the
input parameters in pwscf run?

Regards,
Hengxin

On Fri, Aug 11, 2017 at 8:46 PM, Prasenjit Ghosh <prasenjit.jnc at gmail.com>
wrote:

> Since the hybrid functionals are non ab initio, you can play around with
> the % of EXX to see how that affects the band gap (assuming everything else
> is fine). Or else you can use GGA+U with U on both Zn and O to correct the
> band gap as has been shown in the following paper
>
> J. Phys. Chem. C, * 119 *, 3060 (2015)
>
> and J. Am. Chem. Soc. *133, *5893 (2011).
>
> With regards,
>
> Prasenjit
>
> On 8 August 2017 at 14:54, Tan Hengxin <tanhx90 at gmail.com> wrote:
>
>> Dear all,
>>
>> I am doing some calculations on the HSE06 (25% EXX) band gap of wurtzite
>> ZnO with experimental structure, and find that I cannot get the usual value
>> of ~2.4 eV. My value is just ~2.1 eV.
>> Maybe my norm-conserving pseudopotentials (NC-PPs) of Zn and O are not
>> very good. So I also tried the NC-PPs for Zn and O from the
>> pslibrary.0.3.1. However, the gap is even smaller (~1.8 eV). (All PPs are
>> based on PBE xc.)
>> I have also done different tests with different parameters, containing
>> nbnd, nqx1, nqx2, nqx3, k-mesh. But I still cannot get 2.4 eV for the HSE
>> gap.
>>
>> So could anyone provide a guidance on how to obtain the usual HSE band
>> gap of 2.4 eV for wurtzite ZnO ? The input parameters are as follows, and
>> the output file calculated with the NC-PPs from the pslibrary.0.3.1 is also
>> attached. Thank you in advance!
>>
>> My input parameters for the scf run:
>> &CONTROL
>>   calculation   = 'scf',
>>   prefix        = 'ZnO',
>>   pseudo_dir    = './',
>> ! nstep         = 200,
>>   verbosity     = 'high',
>>   wf_collect    = .true.
>>   etot_conv_thr = 1.0D-5,
>>   forc_conv_thr = 1.0D-4,
>>   restart_mode  = 'from_scratch',
>>   outdir        = './temp_out',
>> /
>> &SYSTEM
>>   ibrav         = 0,
>> ! celldm(1)     = 1.88972688,
>>   nat           = 4,
>>   ntyp          = 2,
>>   ecutwfc       = 60,
>> ! ecutrho       = 240,
>> ! nosym         = .true.
>>   nbnd          = 36,
>> ! occupations   = 'smearing',
>> ! degauss       = 0.000367,
>> ! smearing      = 'gaussian',
>>   input_dft     = 'hse',
>>   exx_fraction  = 0.25,
>> ! screening_parameter = 0.106
>> ! exxdiv_treatment    = gygi-baldereschi
>>   nqx1 = 3, nqx2 = 3, nqx3 = 2,
>> ! nspin         = 2
>> ! starting_magnetization(1) = 1.0,
>> ! starting_magnetization(2) = -1.0,
>> ! lda_plus_u    = .true.
>> ! hubbard_U(5)  = 2.59,
>> ! hubbard_alpha(2) = 0.d0,
>> ! hubbard_U(2)     = 3,
>> /
>> &ELECTRONS
>> ! electron_maxstep = 100,
>>   mixing_mode   = 'plain',
>>   mixing_beta   = 0.7,
>>   conv_thr      = 1.D-8,
>> ! startingwfc   ='atomic+random',
>> ! startingpot   ='atomic',
>> /
>> &IONS
>>   ion_dynamics      = 'bfgs',
>>   pot_extrapolation = 'atomic',
>>   upscale           = 100,
>>   trust_radius_ini  = 0.5,
>> /
>> &CELL
>>   cell_dynamics     = 'bfgs',
>>   press_conv_thr    = 0.5,
>>   cell_dofree       = 'all',
>> /
>>
>> ATOMIC_SPECIES
>>  Zn 65.38     Zn.pbe-nc.UPF
>>  O  15.999    O.pbe-nc.UPF
>>
>> CELL_PARAMETERS (angstrom)
>>      3.249         0.000         0.000
>>     -1.625         2.814         0.000
>>      0.000         0.000         5.205
>>
>> ATOMIC_POSITIONS (crystal)
>> Zn    0.333333343         0.666666687         0.000000000
>> Zn    0.666666627         0.333333313         0.500000000
>> O     0.333333343         0.666666687         0.382600009
>> O     0.666666627         0.333333313         0.882600009
>>
>> K_POINTS {automatic}
>>  9 9 6 0 0 0
>>
>> Regards,
>> Hengxin Tan, PhD
>> Department of Physics
>> Tsinghua University.
>> --
>>
>> Tan Hengxin
>> Department of physics, THU.
>> Beijing 100084, China
>> Office: B403,New Science Building
>> E-mail:t <E-mail%3Athx13 at mails.tsinghua.edu.cn>anhx90 at gmail.com
>>
>>
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>>
>
>
>
> --
> PRASENJIT GHOSH,
> IISER Pune,
> Dr. Homi Bhabha Road, Pashan
> Pune, Maharashtra 411008, India
>
> Phone: +91 (20) 2590 8203
> Fax: +91 (20) 2589 9790
>
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>



-- 

Tan Hengxin
Department of physics, THU.
Beijing 100084, China
Office: B403,New Science Building
E-mail:t <E-mail%3Athx13 at mails.tsinghua.edu.cn>anhx90 at gmail.com
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