[Pw_forum] question about the stress in relax process

[lfhuang]

Dear Wang Di: 
  Are you using Norm-Conserving pseudopotentials? If you are, please increase the ecutwfc to be about 50 Ry or larger, and the density of the k mesh should be high enough (by tests). This is because the accuracy of the calculation of stress is much dependent on the completeness of the plane wave basis set.
    In addition, the forc_conv_thr=1.0d-4 already be great (usually 1.0d-3 is used), smaller thresholds (e.g. 1.0d-6) won't make any difference and only waste much of your invaluable time. And I am very curious about why did you use "dipfield = .true." for your 3D-periodic crystalline system?
 
PS: we are working at the same island (science island), but two institutes, calculating in the same super-computer. I am very glad to meet you on the same Forum :)
 
Best Wishes!
 
Yours Sincerely
L. F. Huang
 
 
> Date: Mon, 20 Sep 2010 14:07:30 +0800 
> From: Wang Di 
> Subject: [Pw_forum] question about the stress in relax process 
> To: PWSCF Forum 
> Message-ID: 
> 
> Content-Type: text/plain; charset="iso-8859-1" 
> 
> Dear all 
> 
> I perform the relax calculate to the crystal structure. After 11 step bfgs, 
> the total force and total scf correction had reach to the criterion, 
> however, the total stress was so big P=-3443.87. I have no idea about deal 
> with the case, could anyone give some advices? Thanks in advance. 
> 
> the input file 
> : &CONTROL 
> calculation = 'scf' , 
> restart_mode = 'from_scratch' , 
> wf_collect = .true. , 
> outdir = '/lustre/AIOFM/gxgu/workLCAF/5/temp/' , 
> wfcdir = '/lustre/AIOFM/gxgu/workLCAF/5/wftemp/' , 
> pseudo_dir = '/home/AIOFM/gxgu/work/NCPP/' , 
> prefix = 'LCAF' , 
> etot_conv_thr = 1.0D-7 , 
> forc_conv_thr = 1.0D-6 , 
> nstep = 100 , 
> tstress = .true. , 
> tprnfor = .true. , 
> dipfield = .true. , 
> / 
> &SYSTEM 
> ibrav = 4, 
> celldm(1) = 9.42432151, 
> celldm(3) = 1.94804220, 
> nat = 18, 
> ntyp = 4, 
> ecutwfc = 30 , 
> ecutrho = 120 , 
> nosym = .false. , 
> / 
> &ELECTRONS 
> electron_maxstep = 100, 
> conv_thr = 1.0D-10 , 
> / 
> ATOMIC_SPECIES 
> Li 6.94100 03-Li.LDA.fhi.UPF 
> Al 26.98154 13-Al.LDA.fhi.UPF 
> Ca 40.07800 20-Ca.LDA.fhi.UPF 
> F 18.99840 09-F.LDA.fhi.UPF 
> ATOMIC_POSITIONS crystal 
> Li 0.333333333 0.666666667 0.250000000 
> Li -0.333333333 -0.666666667 -0.250000000 
> F 0.389997 0.045970 0.148326 
> F -0.045970 0.344027 0.148326 
> F -0.344027 -0.389997 0.148326 
> F -0.045970 -0.389997 0.351674 
> F -0.344027 0.045970 0.351674 
> F 0.389997 0.344027 0.351674 
> F -0.389997 -0.045970 -0.148326 
> F 0.045970 -0.344027 -0.148326 
> F 0.344027 0.389997 -0.148326 
> F 0.045970 0.389997 0.648326 
> F 0.344027 -0.045970 0.648326 
> F -0.389997 -0.344027 0.648326 
> Al 0.666666667 0.333333333 0.250000000 
> Al -0.666666667 -0.333333333 -0.250000000 
> Ca 0.000000000 0.000000000 0.000000000 
> Ca 0.000000000 0.000000000 0.500000000 
> K_POINTS automatic 
> 16 16 16 0 0 0 
> 
> best regart 
> 
> Wang Di 
> 
> -- 
> ----------------------------------------------------------------- 
> *Wang Di** 
> The Crystal Lab,* 
> *AnHui Institute of Optics and Fine Mechanics, *** 
> *Chinese Academy of Sciences,** 
> No350. , Shushanhu Road, Hefei, 230031, China**, 
> E-mail: didi5158 @gmail.ocm** ,* 
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------ 
====================================================================== 
L.F.Huang(黄良锋) DFT and phonon physics 
====================================================================== 
Add: Research Laboratory for Computational Materials Sciences, 
Instutue of Solid State Physics,the Chinese Academy of Sciences, 
P.O.Box 1129, Hefei 230031, P.R.China 
Tel: 86-551-5591464-326(office) 
Fax: 86-551-5591434 
Our group: http://theory.issp.ac.cn 
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