[Wien] optimization/minimization

[Jeff Spirko]

Read the Wien2k manual section on the lapw2 program, run_lapw,
min_lapw, and mini.

Normally, one is concerned with the energy, and forces are only
calculated in a quick way (TOT is set on line 1 of case.in2).  But if
you need accurate forces, for example for an optimization, then an
additional correction term needs to be calculated.  To get this, FOR
must be set.  But, the Pulay term isn't needed for the convergence
test, only for the final result.  So it can waste time to just leave
FOR set for the entire run.

Looking more deeply, there are several ways the force setting gets
set.

1.  Manually, you can edit case.in2 or case.in2c.  But it may get
    changed as described below.

2.  run_lapw -I will set TOT at the beginning.  This allows for the
    possibility of a quick force calculation until convergence.

3.  "run_lapw -fc x" will make sure that FOR gets set for the last
    iteration.  Therefore, upon successful exit the correct forces are
    calculated.

Use both -I and -fc x and you get the best of both worlds, faster
pre-convergence calculations and correct forces in the end.

Regards,
-Jeff Spirko


On Mon, Jan 02, 2006 at 04:48:42PM +0800, yxl at email.jlu.edu.cn wrote:
> Dear Jeff ,
>   Would you be kind enough to explain for me what you've said"
> If you set your own job with 'min_lapw -j "runsp_lapw ..."', it is
> important during a minimization that the full forces be calculated.
> This requires FOR to be set at the beginning of case.in2[c] for at
> least the last iteration.  "
> I want to know why? Thank you very much ! 
>                                        yours sincerely
>                                          hong xia
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-- 
Jeff Spirko   spirko at lehigh.edu   spirko at yahoo.com   WD3V   |=>

The study of non-linear physics is like the study of non-elephant biology.

All theoretical chemistry is really physics;
and all theoretical chemists know it. -- Richard P. Feynman