[Wien] How to speed up a reliable optimization

[Luis Ogando]

Dear Prof. Marks,

   Thank you very much for your answers ! I am pretty sure that your
"intuition" will save a lot of computation time !
   Just one last question: I have another system , a supercell formed by 15
InP zinc blend cells along [111] (hexagonal representation of the cubic
lattice) and 3 InP wurtzite cells. They are aligned along the hexagonal "c"
axis.
                                     Comparing the gaps of the respective
bulks and this supercell (same calculation parameters) , I believe that the
SCF cycle (here, it is not a lattice optimization) stopped at a local
minimum.
                                      My question is : in this case
(regular SCF cycle and InP cells), would you change any of your previous
answers ?
   Thank you again !!
   All the best,
                 Luis


2017-01-25 17:56 GMT-02:00 Laurence Marks <L-marks at northwestern.edu>:

> 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
>
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