[Pw_forum] Relaxation doesn't converge

[Huiqun Zhou]

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
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