[Pw_forum] Fw: relax is too slow

vega vegalew at hotmail.com
Fri Sep 12 11:26:01 CEST 2008


 
>I think it is the too much k-points that caused the problem .when I set the k-point to Gamma ,it iterated very quickly.but I don't know whether it is right or wrong that I set it to Gamma.

I don't know either. I think you could compare the Gamma results and 2X2X2 or 4X4X4 if necessary. If the energy different and coordinate is nearly the same. you may could use a small K-mesh to save computional cost. 
As far as I tested, the energy would be within 1% for large supercells, but the coordinates of several atoms may differ 200%. So I have the same question like you. 
Could anyone help us, please~ what is the benchmark for judging whether the k-mesh is adequate? the most important thing is the energy or the coordinates of atoms? If the energy difference is with 1% and 80% of atoms or more in the system is nearly at the same position, but coordinate some of atoms very different for the two case. Could we trust the results calculated by relative small number of k points?

 vega
=================================================================================
Vega Lew (weijia liu)
PH.D Candidate in Chemical Engineering
State Key Laboratory of Materials-oriented Chemical Engineering
College of Chemistry and Chemical Engineering
Nanjing University of Technology, 210009, Nanjing, Jiangsu, China


From: wangqj1 
Sent: Friday, September 12, 2008 3:34 PM
To: vegalew at hotmail.com 
Subject: relax is too slow




 Thank you very much for your advice !
My input file as follows:
  &CONTROL
                       title = ZnOrelax ,
                 calculation = 'relax' ,
                restart_mode = 'from_scratch' ,
                  pseudo_dir = '/root/tool/espresso-3.2.3/pseudo/' ,
                      prefix = ZnO ,
               forc_conv_thr = 1.D-4 ,
                     tstress = .true. ,
                     tprnfor = .true. ,
                          dt = 100 ,
 /
 &SYSTEM
                       ibrav = 14,
                   celldm(1) = 18.6488,
                   celldm(2) = 0.666667,
                   celldm(3) = 1.0691,
                   celldm(4) = 0,
                   celldm(5) = 0,
                   celldm(6) = -0.5,
                         nat = 48,
                        ntyp = 2,
                     ecutwfc = 40 ,
                     ecutrho = 200 ,
                       nosym = .true. ,
                        nbnd = 220,
                 occupations = 'smearing' ,
                     degauss = 0.002 ,
                    smearing = 'methfessel-paxton' ,
                       nspin = 1 ,
                  lda_plus_u = .false. ,
 /
 &ELECTRONS
                 startingpot = 'atomic' ,
                 startingwfc = 'atomic' ,
                 mixing_mode = 'plain' ,
                 mixing_beta = 0.7 ,
             diagonalization = 'cg' ,
 /
 &IONS
                ion_dynamics = 'damp' ,
                 phase_space = 'full' ,
           pot_extrapolation = 'second_order' ,
           wfc_extrapolation = 'second_order' ,
 /
ATOMIC_SPECIES
   Zn   65.00000  Zn.pbe-van.UPF 
    O   16.00000  O.pbe-rrkjus.UPF 
ATOMIC_POSITIONS angstrom 
   Zn      0.000000000    1.899193710    0.000000000    1  1  1 
    O      0.000000000    1.899193710    2.018253260    1  1  1 
   Zn      1.644750000    0.949596855    2.637550000    1  1  1 
    O      1.644750000    0.949596855    4.655803260    1  1  1 
   Zn      3.289500000    1.899193710    0.000000000    1  1  1 
    O      3.289500000    1.899193710    2.018253260    1  1  1 
   Zn      4.934250000    0.949596855    2.637550000    0  0  0 
    O      4.934250000    0.949596855    4.655803260    0  0  0
   Zn      6.579000000    1.899193710    0.000000000    0  0  0 
    O      6.579000000    1.899193710    2.018253260    0  0  0 
   Zn      8.223750000    0.949596855    2.637550000    0  0  0 
    O      8.223750000    0.949596855    4.655803260    0  0  0 
   Zn     -1.644750000    4.747984276    0.000000000    1  1  1 
    O     -1.644750000    4.747984276    2.018253260    1  1  1 
   Zn      0.000000000    3.798387421    2.637550000    1  1  1 
    O      0.000000000    3.798387421    4.655803260    1  1  1 
   Zn      1.644750000    4.747984276    0.000000000    1  1  1 
    O      1.644750000    4.747984276    2.018253260    1  1  1 
   Zn      3.289500000    3.798387421    2.637550000    0  0  0 
    O      3.289500000    3.798387421    4.655803260    0  0  0 
   Zn      4.934250000    4.747984276    0.000000000    0  0  0 
    O      4.934250000    4.747984276    2.018253260    0  0  0 
   Zn      6.579000000    3.798387421    2.637550000    0  0  0 
    O      6.579000000    3.798387421    4.655803260    0  0  0 
   Zn      0.000000000    1.899193710    5.275100000    1  1  1 
    O      0.000000000    1.899193710    7.293353260    1  1  1 
   Zn      1.644750000    0.949596855    7.912650000    1  1  1 
    O      1.644750000    0.949596855    9.930903260    1  1  1 
   Zn      3.289500000    1.899193710    5.275100000    1  1  1 
    O      3.289500000    1.899193710    7.293353260    1  1  1 
   Zn      4.934250000    0.949596855    7.912650000    0  0  0 
    O      4.934250000    0.949596855    9.930903260    0  0  0 
   Zn      6.579000000    1.899193710    5.275100000    0  0  0 
    O      6.579000000    1.899193710    7.293353260    0  0  0 
   Zn      8.223750000    0.949596855    7.912650000    0  0  0 
    O      8.223750000    0.949596855    9.930903260    0  0  0 
   Zn     -1.644750000    4.747984276    5.275100000    1  1  1 
    O     -1.644750000    4.747984276    7.293353260    1  1  1 
   Zn      0.000000000    3.798387421    7.912650000    1  1  1 
    O      0.000000000    3.798387421    9.930903260    1  1  1 
   Zn      1.644750000    4.747984276    5.275100000    1  1  1 
    O      1.644750000    4.747984276    7.293353260    1  1  1 
   Zn      3.289500000    3.798387421    7.912650000    0  0  0 
    O      3.289500000    3.798387421    9.930903260    0  0  0 
   Zn      4.934250000    4.747984276    5.275100000    0  0  0 
    O      4.934250000    4.747984276    7.293353260    0  0  0 
   Zn      6.579000000    3.798387421    7.912650000    0  0  0 
    O      6.579000000    3.798387421    9.930903260    0  0  0 
K_POINTS automatic 
  4 4 4   0 0 0 

According your advice I found the CPU user% ratio is about 98% and the swap is about 16%.I think it is the too much k-points that caused the problem .when I set the k-point to Gamma ,it iterated very quickly.but I don't know whether it is right or wrong that I set it to Gamma.

Sincerely
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