[Pw_forum] force convergence in vc-relax

[Tianli Feng]

Hi Florian, I have not got the issue resolved yet.

Hi Paolo, How can we find the explanation in that code? Many thanks.

Best wishes,
Tianli
------------
Tianli Feng
Mechanical Engineering, Purdue University
---The truth is not what you see, but what it is.

On Mon, Apr 13, 2015 at 4:10 AM, Paolo Giannozzi <paolo.giannozzi at uniud.it>
wrote:

> On Mon, 2015-04-13 at 00:16 -0700, Florian Altvater wrote:
>
> > did this issue ever get resolved/answered? I would also be very
> > interested in a solution/explanation of the behavior.
>
> The explanation is available in the part of code that perform the
> convergence check on forces
>
> P.
> > I also get relaxations where individual forces are higher than the
> > threshold, without the line stating that "SCF correction compared to
> > forces is large", in case that would be a reason here. Also happens in
> > regular "relax" calculations.
> >
> > Thanks so much,
> > Florian
> >
> > --
> > Florian Brown-Altvater
> > PhD Candidate
> > Neaton group
> > UC Berkeley/LBNL
> >
> > Am 08.04.2015 um 12:07 schrieb Tianli Feng:
> >
> > > Dear All,
> > >
> > >
> > > I would really appreciate if anyone can help to explain a output in
> > > relaxing a structure. I used vc-relax to relax a lattice
> > > with forc_conv_thr set as 1.0D-9. After 44 steps, the results
> > > converge as following:
> > >
> > >
> > >      Forces acting on atoms (Ry/au):
> > >
> > >
> > >      atom    1 type  1   force =     0.00000638    0.00000000
> > >  0.00000092
> > >      atom    2 type  1   force =     0.00000602    0.00000000
> > >  0.00000671
> > >      atom    3 type  1   force =    -0.00000074    0.00000000
> > >  0.00000243
> > >      atom    4 type  1   force =     0.00000358    0.00000000
> > > -0.00000082
> > >      atom    5 type  2   force =    -0.00000821    0.00000000
> > > -0.00000732
> > >      atom    6 type  2   force =    -0.00000635    0.00000000
> > > -0.00000202
> > >      atom    7 type  2   force =     0.00000337    0.00000000
> > > -0.00000058
> > >      atom    8 type  2   force =    -0.00000406    0.00000000
> > >  0.00000068
> > >
> > >
> > >      Total force =     0.000018     Total SCF correction =
> > > 0.000002
> > >      SCF correction compared to forces is large: reduce conv_thr to
> > > get better values
> > >
> > >
> > >      bfgs converged in  44 scf cycles and  43 bfgs steps
> > >      (criteria: energy <  1.0E-04, force <  1.0E-09, cell <
> > >  5.0E-01)
> > >
> > >
> > > The last line says the relaxation converges with force <1.0E-9, but
> > > I saw the forces acting on each atom are not smaller than 1e-9. Does
> > > anyone has experience on relaxing a lattice and know what is
> > > happening? Many thanks!!
> > >
> > >
> > > Sincerely,
> > > Best wishes,
> > > Tianli
> > > ------------
> > > Tianli Feng
> > > Mechanical Engineering, Purdue University
> > > ---The truth is not what you see, but what it is.
> > >
> > >
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>
> --
>  Paolo Giannozzi, Dept. Chemistry&Physics&Environment,
>  Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
>  Phone +39-0432-558216, fax +39-0432-558222
>
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