[QE-users] [SPAM] Sharp peaks at the band structure calculated with hybrid functional using the "fake" procedure

[Lorenzo Paulatto]

Hello,

I agree with you that the procedure sometimes works, sometimes it does 
not. I think the problem is that the wavefunctions at the points with 
zero weight have no variational constraint, and depending of the linear 
algebra used can converge to something sensible or not. One could try to 
modify additional_kpoint.f90 and set some small but non zero weight to 
the additional points (something in the 10^-6 to 10^-10 range). And then 
renormalize the sum of the weights.

Can you try (and most importantly test) this yourself? I won't be able 
to do any programming before a few weeks.

There are only a couple of line to change:

wk(nkstot_old+1:nkstot_old+nkstot_add) =0._dp

then, the other case :
wk(iq)=0.0d0


Instead of zero, you put a small constant. At the end, add something like
     aux = SUM(wk)
    CALL mp_sum(aux, intra_pool_sum)
    wk = wk/aux

hth

On 29/07/2022 21:49, Антон Андреевич Гавриков wrote:
> Dear colleagues,
> we have tried to perfom band structure DFT-calculation of crystall 
> SrTiO3 with hybrid functionals.
> When we run tests with silicon from the QE package it was OK.
> But when we tried SrTiO3 following to the "fake" procedure in Si 
> example, we've got sharp peaks in band structure graph.
> We have used PBE0 and HSE functionals with US pseudopotentials. The 
> result was the same.
> Furthermore, despite we used  nqx1 = 2  nqx2 = 2  nqx3 = 2 in scf-input,
> in scf-output there is the record:  EXX: q-point mesh:   1    1    1
> Input-file:
> &CONTROL
>   calculation = "scf"
>   restart_mode='from_scratch',
>   prefix = 'SrTiO3',
>   nstep       = 900,
>   max_seconds =  8.64000e+04
>   pseudo_dir  = "/home/QuantumEspresso/pseudo",
>   wf_collect = .true.
>   etot_conv_thr   =  1.0d-8
>   verbosity ='high'
> /
> &SYSTEM
>     ibrav  = 1,
>     a =  3.8931e+00,
>     nat=5,
>     ntyp=3,
>     occupations='smearing',
>     smearing   ='gauss',
>     degauss    = 0.005,
>     nspin= 1
>     ecutwfc = 55.0d0
>     ecutrho = 580.d0
>     input_dft = 'hse',
>     nqx1 = 2
>     nqx2 = 2
>     nqx3 = 2
> /
> &ELECTRONS
>     electron_maxstep = 800
>     conv_thr         =  1.0d-8
>     mixing_beta      =  0.3
> /
> &IONS
> ion_dynamics ='bfgs'
> /
> &CELL
> /
> ATOMIC_SPECIES
> O     15.9994  O.pbesol-n-rrkjus_psl.1.0.0.UPF
> Sr    87.6200  Sr.pbesol-spn-rrkjus_psl.1.0.0.UPF
> Ti    47.8670  Ti.pbesol-spn-rrkjus_psl.1.0.0.UPF
> ATOMIC_POSITIONS {crystal}
>    O           0.5           0.0           0.5
>    O           0.5           0.5           0.0
>    O           0.0           0.5           0.5
>    Sr          0.0           0.0           0.0
>    Ti           0.5           0.5           0.5
> K_POINTS automatic
>  8 8 8 0 0 0
> ADDITIONAL_K_POINTS tpiba_b
>  8
>    0.0000000000     0.0000000000     0.0000000000   20 ! GAMMA
>    0.0000000000     0.5000000000     0.0000000000   20 ! X
>    0.5000000000     0.5000000000     0.0000000000   28 ! M
>    0.0000000000     0.0000000000     0.0000000000   36 ! GAMMA
>    0.5000000000     0.5000000000     0.5000000000   28 ! R
>    0.0000000000     0.5000000000     0.0000000000    0 ! X
>    0.5000000000     0.5000000000     0.0000000000   20 ! M
>    0.5000000000     0.5000000000     0.5000000000    0 ! R
> Would you answer my question, is there a way to get appropriate band 
> structure picture with hybrid functional using the "fake" procedure?
> Regards,
> Gavrikov Anton,
> PhD, researcher,
> Saint-Petersburg State University.
>
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-- 
Dr. Lorenzo Paulatto
IdR @ IMPMC - CNRS UMR 7590 & Sorbonne Université
phone: +33 (0)1 442 79822 / skype: paulatz
http://www.impmc.upmc.fr/~paulatto/ - https://anharmonic.github.io/
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