[Pw_forum] Relaxation doesn't converge

[程迎春]

In my opinion, the stricter the criterion, the more ecut and more K points
sampling.

2009/9/2 Huiqun Zhou <hqzhou at nju.edu.cn>

> Pablo,
>
> Usually, setting conv_thr = 1d-8 is sufficient, please make sure if you
> need such strict convergence criterion.
>
>
> Huiqun Zhou
> @Earth Sciences, Nanjing University, China
>
>
> ----- Original Message -----
> From: "Pablo Aguado" <paguado at gmail.com>
> To: <pw_forum at pwscf.org>
> Sent: Tuesday, September 01, 2009 6:38 PM
> Subject: [Pw_forum] Relaxation doesn't converge
>
>
> > Dear all,
> >
> > I'm doing some tests on the structural optimization with pw. I'm
> > currently testing with the tetragonal structure of PbTiO3, using the
> > following input:
> >
> > &control
> >    calculation  = 'vc-relax'
> >    restart_mode = 'restart'
> >    pseudo_dir   = '/****/espresso-4.1/pseudo/'
> >    outdir       = '/***/tmp'
> >    forc_conv_thr = 1d-3
> >    nstep = 50
> > /
> > &system
> >    ibrav=6
> >    celldm(1)=7.3699
> >    celldm(3)=1.04
> >    nat=5
> >    ntyp=3
> >    nbnd=28
> >    ecutwfc=30.0
> >    occupations = 'fixed'
> > /
> > &electrons
> >    conv_thr = 1d-12,
> >    mixing_beta=0.4,
> > /
> > &ions
> >    ion_dynamics = 'bfgs'
> >    bfgs_ndim = 5
> > /
> > &cell
> >    cell_dynamics = 'damp-pr'
> >    press_conv_thr = 1.0d0
> >    cell_dofree = 'z'
> > /
> > ATOMIC_SPECIES
> >  Pb   207.2      Pb.pz-d-van.UPF
> >  Ti    47.867    Ti.pz-sp-van_ak.UPF
> >  O     15.9994   O.pz-van_ak.UPF
> > ATOMIC_POSITIONS crystal
> >  Pb    0.000    0.000    0.040   0 0 1
> >  Ti    0.500    0.500    0.520   0 0 1
> >  O     0.000    0.500    0.500   0 0 1
> >  O     0.500    0.500    0.000   0 0 1
> >  O     0.500    0.000    0.500   0 0 1
> > K_POINTS automatic
> >  6 6 6 1 1 1
> >
> > The relaxation is taking forever so I've checked the output and I've
> > found several steps where everything seems to be converged (notice I'm
> > only relaxing out-of-plane lattice vector) but the code keeps running.
> > An example:
> >
> > - Energy difference = 4e-7
> > - Forces acting on atoms (Ry/au):
> >
> >     atom   1 type  1   force =     0.00000000    0.00000000    0.00085679
> >     atom   2 type  2   force =     0.00000000    0.00000000   -0.00001779
> >     atom   3 type  3   force =     0.00000000    0.00000000   -0.00024617
> >     atom   4 type  3   force =     0.00000000    0.00000000   -0.00034665
> >     atom   5 type  3   force =     0.00000000    0.00000000   -0.00024617
> >
> >     Total force =     0.000988     Total SCF correction =     0.000002
> >
> >          total   stress  (Ry/bohr**3)                   (kbar)
> >   P=   -0.84
> >  -0.00001150   0.00000000   0.00000000         -1.69      0.00      0.00
> >   0.00000000  -0.00001150   0.00000000          0.00     -1.69      0.00
> >   0.00000000   0.00000000   0.00000591          0.00      0.00      0.87
> >
> > Any idea of what's going on?
> >
> > Thank you very much
> >
> > Pablo
> > _______________________________________________
> > Pw_forum mailing list
> > Pw_forum at pwscf.org
> > http://www.democritos.it/mailman/listinfo/pw_forum
> >
>
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-- 
Y. C. Cheng
Department of Physics
Nanjing University
Nanjing 210093
P. R. China
Tel: 86-25-83592907
Email: yccheng.nju at gmail.com
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