[Pw_forum] testing HSE for BCC Fe

[Daniel Stoeffler]

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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>> Pw_forum at pwscf.org
>>
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> 
>
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