[Wien] How to speed up a reliable optimization

[Laurence Marks]

Inlined is my intuition, which does not have to be completely right.

On Wed, Jan 25, 2017 at 11:32 AM, Luis Ogando <lcodacal at gmail.com> wrote:

> Dear Prof. Marks (and Wien2k community),
>
>    After a recent discussion about "difficult" optimizations in this
> mailing list (subject: "Mixer surprise when using PBE0 hybrid on-site
> functional"), I would like ask you for an advice.
>    I have a system with:
> * 5 rings with C, H and N atoms
> * 100 atoms with P1 symmetry
> * the rings are out of a plane
> * vacuum along y and z
>    I know that this is a very hard optimization problem, so I would like
> to kindly ask:
>
> 1) Do you believe that MSEC3a will work better than MSR1a in such a case ?
>

I would switch to MSEC3a, use SLOW or reduce the GREED to 0.1 only if you
see indications of problems. If the system is a decent insulator and the
experimental positions are quite good you may have no problems. At the end
I would switch back to MSR1a certainly for a system with OH as the
positions of the hydrogens can be quite soft. It can take quite some time
to get the rotations of the OH bond distance right as Wien2k uses cartesian
coordinates not polars. Which of the 3 is best -- I am not sure.

>
> 2) Do you recommend using -it, -vec2pratt and -noHinv options with
> run_lapw ?
>

I use -it -noHinv -vec2pratt. Sometimes you need to do an occasional full
diagonalization (touch .fulldiag) as the iterative method is less stable
(it adds a little noise). In my personal version I have added back the old
-itn option so this is done automatically every few steps.

>
> 3) Should I reduce TRUST to 0.5 (I am using LDA and experimental values
> for the initial atomic positions) ?
>

Probably not. TRUST 0.5 would be if it is taking much too large steps which
tends (in my experience) to occur more with soft electronic modes such as
one has with d and f electrons.

>
> 4) Should I use SLOW in case.inm ?
>

See my answer to 1)

>
>    Many thanks in advance.
>    All the best,
>                       Luis
>
>


-- 
Professor Laurence Marks
"Research is to see what everybody else has seen, and to think what nobody
else has thought", Albert Szent-Gyorgi
www.numis.northwestern.edu ; Corrosion in 4D: MURI4D.numis.northwestern.edu
Partner of the CFW 100% program for gender equity, www.cfw.org/100-percent
Co-Editor, Acta Cryst A
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://zeus.theochem.tuwien.ac.at/pipermail/wien/attachments/20170125/431b9265/attachment.html>