[Pw_forum] testing HSE for BCC Fe

Stefano de Gironcoli degironc at sissa.it
Fri Sep 9 09:47:22 CEST 2016


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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