[Pw_forum] testing HSE for BCC Fe

[Daniel Stoeffler]

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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