[Pw_forum] testing HSE for BCC Fe
Giuseppe Mattioli
giuseppe.mattioli at ism.cnr.it
Fri Sep 9 11:50:35 CEST 2016
Dear Daniel, Stefano and Paolo.
My added penny: in my hands US/EXX has never worked in a useful way...:-( Moreover there is a nasty constraint that force ecutrho=4*ecutwfc, that is
not exactly the best for US PPs.
It might turn out that a NC/EXX calculation (always very satisfying in my hands) is significantly faster end quite reliable, even if you must use
80/320 Ry cutoffs (or even higher; first row transition metals with 2s,2p semicore electrons are usually the hardest NC PPs).
You can try to speedup the calculation by using
a) adaptive_thr=.true.
In the case of smooth convergence this makes inner scf cycles significantly faster.
b) ecutfock~[1/2-->1/4]*ecutrho
Fantastic with isolated systems; handle with care with metals because this might change occupations at k-points. You should check convergence on this,
but in the case of "almost metallic" systems (e.g., shallow defects in semiconductors) ecutfock=1/2*ecutrho is often well converged.
c) remember that (at least in principle) you should check convergence with respect to the projection of density in real space: you are (implicitly)
using one q-point for each k-point, having not assigned any value to nqx1, nqx2, nqx3. More q points increase the computational effort. You might try
to reduce the k grid and to increase nqx(i) values to find a correct balance: However a 7 7 7 0 0 0 grid is actually large. You will not be able to
perform 'nscf' or 'bands' calculations to have a proper band structure, and densities/forces/stresses/eigenvalues/energies should converge at an
acceptable level with less k points.
HTH
Giuseppe
On Friday, September 09, 2016 10:42:49 AM Daniel Stoeffler wrote:
> Hello Stefano,
>
> As said, I am a new user of QE but not of the DFT
> ;). I use the FLEUR, Abinit and the VASP codes and I want to test if it
> would be interesting for my studies to use also QE.
>
> I said
> "surprisingly" huge because I compared to the VASP code with the same
> parameters (Ecutoff, NKpoints, Nq) and with the HSE functional. Indeed,
> with the VASP code during one night on my computer I got a few tens of
> iterations compared to one with QE :(.
>
> >From my point of view, I
>
> compare 2 pseudopotential-based methods for the same parameters which I
> can control via the input file : my question would then more preferably
> be "which default parameter should I modify to make the QE calculation
> time similar to the VASP one ?"
>
> Best wishes,
>
> Daniel
>
> Le 2016-09-09
>
> 09:47, Stefano de Gironcoli a écrit :
> > Please read the literature
>
> about hybrid functionals in plane waves; understand why the
> computational time is, not unexpectedly, huge and start think about it.
>
> > If you come up with some smart idea on how to reduce the
>
> computational time without compromising accuracy (as for the ACE
> transformation recently proposed by Lin Lin and implemented in the
> latest QE version) let us know
>
> > Best,
> > stefano
> > (sent from my phone)
> >
> >
> > On 09 Sep 2016, at 09:30, Daniel Stoeffler
>
> <daniel.stoeffler at ipcms.unistra.fr> wrote:
> >> Hello,
> >>
> >> As a new
>
> QE user, I do some tests with the HSE Functional for BCC ferromagnetic
> Fe with a cell containing 2 atoms (because a want to go to CoFe after
> that).
>
> >> My input file is :
> >>
> >> &control
> >> title='Fe CC
>
> HSE',
>
> >> calculation = 'scf',
> >> prefix = 'Fe_CC_HSE',
>
> pseudo_dir='./',
>
> >> verbosity = 'high'
> >> /
> >> &system
> >> ibrav = 6,
>
> celldm(1) = 5.45,
>
> >> celldm(3) = 1.0,
> >> nat = 2,
> >> ntyp = 1,
>
> nspin = 2,
>
> >> occupations='smearing', smearing='gauss', degauss=0.01,
>
> starting_magnetization(1) = 1.0,
>
> >> ecutwfc = 33,
> >> input_dft='HSE',
> >>
> >> report = 5
> >> /
> >> &electrons
> >> mixing_beta = 0.7
> >> /
>
> ATOMIC_SPECIES
>
> >> Fe 55.845 Fe.pbe-sp-van.UPF
> >>
> >> ATOMIC_POSITIONS
>
> (crystal)
>
> >> Fe 0.000 0.000 0.000
> >> Fe 0.500 0.500 0.500
>
> K_POINTS (automatic)
>
> >> 7 7 7 0 0 0
> >>
> >> Surprisingly, the computation
>
> time is huge as writen into the output file :
>
>
> ===============================
>
> >> iteration # 9 ecut= 33.00 Ry
>
> beta=0.70
>
> >> Davidson diagonalization with overlap
> >> ethr = 5.49E-08,
>
> avg # of iterations = 2.3
>
> >> Magnetic moment per site:
> >> atom: 1
>
> charge: 14.4350 magn: 2.6346 constr: 0.0000
>
> >> atom: 2 charge: 14.4351
>
> magn: 2.6343 constr: 0.0000
>
> >> total cpu time spent up to now is 7.2
>
> secs
>
> >> End of self-consistent calculation
> >>
> >> convergence has
>
> been achieved in 9 iterations
>
> >> EXX: now go back to refine exchange
>
> calculation
>
> >> total cpu time spent up to now is 4239.4 secs
>
> Self-consistent Calculation
>
> >> iteration # 1 ecut= 33.00 Ry
>
> beta=0.70
>
> >> Davidson diagonalization with overlap
> >> ethr = 5.49E-08,
>
> avg # of iterations = 4.9
>
> >> total cpu time spent up to now is
>
> 52490.2 secs
>
> >> iteration # 2 ecut= 33.00 Ry beta=0.70
> >> Davidson
>
> diagonalization with overlap
>
> >> ===============================
> >>
> >>
> >> So, the calculation takes 7 seconds for converging with PBE, 1h10min
>
> for calculating the EXX term and 14h35min for the first HSE iteration.
> Is this correct ? And if so, please, could you try to explain me how to
> reduce the computation time. Thanks in advance.
>
> >> Best wishes,
> >>
> >>
> >> Daniel
> >>
> >> _______________________________________________
>
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>
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>
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>
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Giuseppe Mattioli
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