[Pw_forum] testing HSE for BCC Fe

[dario rocca]

Dear Daniel

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 :(.
>

With exactly the same parameters the computational time (on one processor)
should be comparable. There are two important points you should consider to
make a comparison:
-Different type of methodology: Using EXX with Ultrasoft pseudopotentials a
very large number of augmentation charges are computed. As already
suggested setting tqr=.true. should solve this problem.
-If you changed the default values of some variables such as Precfock or
Nkred in Vasp the computational parameters are not anymore the same in Vasp
and QE.
Best,
Dario




> 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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