[Pw_forum] Calculation Precision on QE5.0.2-GPU

[Tobin Chen]

hi everyone:
    It's my first time to use QE, and I meet some problems that I don't
know how to handle it.
    *DESCRIPTION*
    At first, I compile the QE5.0.2 without GPU. And I use pw.x to run my
relax.in(attach at the end), using the command:
        *[PATH_TO_QE]/bin/pw.x -in relax.in <http://relax.in/>*
    By this version, I can run relax.in to the end.
    However, when I recompile QE with Nvidia GPU (QE-GPU-r216.tar.gz with
the QE-5.0.2_GPU-r216.patch, and I use CUDA5.5), I meet the one of the Frequent
errors during execution<http://www.quantum-espresso.org/faq/frequent-errors-during-execution/>,
which is
        *%%%%%%%*
*            Error in routine electrons (1):*
*            charge is wrong*
*        %%%%%%%*
    So I change the input file by comment some settings on SYSTEM modules.
*        !  occupations='smearing',smearing='gaussian',degauss=0.002,*
*        !  nspin=2*
    And then I can run it on my gpu host, using my gpu card. For this
situation, I guess the "*gaussian **smearing" *may lost some precision on
GPU calculation. But I'm not sure that.

*    QUESTION*
    I feel confused of this situation. My question is
    1, Is the GPU's precision not support for  some of the QE workload? or
just some algorithms?
    2, If it's just for the algorithms problem, which algorithm would be
affect during calculating on GPU version? How should I do when I want to
use GPU to accelera the QE-CPU version?
    3, The last question is, what changes would happen to the final result
when I modify the parameter "*occupations" *and* "**smearing**"*? Just like
the PW/tests/check-pw.x.j, if I don't have the reference, How can I check
whether my result is true when I calculate for the new workload?

    Thanks for everyone ! Maybe my chinglish would confuse you, but please
report it to me. Because I really want you help !
    Thank you very much !

-- 
Tobin Chen
Sun Yat-Sen University <http://www.sysu.edu.cn/>, Guangdong, China.

*file relax.in <http://relax.in/>*
&control
   calculation = 'vc-relax'
   prefix='Na2Fe2As2O',
   pseudo_dir
='/home/jin/projects/asc14/suanli/test2/workload1/workload2-upf'
   outdir='./tmp'
        etot_conv_thr = 1.0E-5 ,
        forc_conv_thr = 1.0D-4
   tprnfor=.TRUE.
   disk_io='none'
/
&system
   ibrav=7,
   celldm(1) =7.691188393, celldm(3)=3.756265356,
   nat=7, ntyp=5,
   ecutwfc=40, ecutrho=480,
   occupations='smearing',smearing='gaussian',degauss=0.002,
   nspin=2
   starting_magnetization(2)=0.125
   starting_magnetization(3)=-0.125
!  nbnd=35
!  lda_plus_u=.TRUE.
!  Hubbard_U(2)=6.0
/
&electrons
   electron_maxstep=300
   mixing_beta = 0.3
   conv_thr =  1.0d-10
/
&ions
  bfgs_ndim= 3,
  ion_dynamics='bfgs'
  pot_extrapolation = 'second_order' ,
  wfc_extrapolation = 'second_order'
/
&CELL
  cell_dynamics = 'bfgs'
/
ATOMIC_SPECIES
Na   22.99  Na.pw91-sp-van_ak.UPF
Fe1  55.845 Fe.pw91-sp-van_ak.UPF
Fe2  55.845 Fe.pw91-sp-van_ak.UPF
As   74.92  As.pw91-n-van.UPF
O     16.00  O.pw91-van_ak.UPF
ATOMIC_POSITIONS {angstrom}
Na      0.0000000000     0.0000000000     4.7989032000
Na      0.0000000000     0.0000000000    10.4890968000
Fe1     0.0000000000    -2.0350000000     7.6440000000
Fe2     2.0350000000     0.0000000000     7.6440000000
As      0.0000000000     0.0000000000     1.8529056000
As      0.0000000000     0.0000000000    13.4350944000
O       0.0000000000     0.0000000000     7.6440000000
K_POINTS {automatic}
4 4 4 1 1 1
npool=2
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