[Wien] The new method of optimizing the internal parameter

[Laurence Marks]

There is in my opinion no "right" method. The question is what are you
trying to do?

Case 1: A structure with fixed positions or a problem where you "don't
care" about minor forces, e.g. calculating a simple bulk structure. Then
just "runsp -cc 0.0001 -ec 0.0001" is fine. (I prefer to use -cc as well as
the default -ec).

Case 2: A simple structure where there might be minor forces that you do
care about. Then something like "runsp -cc 0.0001 -ec 0.0001 -fc 1" first
and check the forces. Iff they are too large for you, then "save -f -d
PreMin ; runsp -cc 0.001 -ec 0.0001 -min" or similar.

Case 3: A more complex structure where you know the positions are not quite
right. I suggest using something like
runsp -cc 0.01 -ec 0.1 -fc 4
save -f -d PreMin
runsp -cc 0.001 -ec 0.0001 -fc 1 -min

This avoids converging too much at first when you know the result won't be
right until the internal minimization has been done. In addition, MSR1a
often works better when started from a partial minimization where the
density and pseudo-charges are somewhat converged. For a large problem add
"-noHinv", I have had problems with -min and -it in the past.

On Mon, Oct 15, 2018 at 9:03 AM karima Physique <physique.karima at gmail.com>
wrote:

> Dear Wien2k user;
>
> According to user guide, after a SCF cycle with runsp -fc 1 we continue
> with  run runsp -min
> I want to know which of these two methods is the correct one:
> 1)
> runsp -fc 1
> runsp -min
> runsp -min -fc 0.5 -ec 0.0001 -cc 0.001
>
> or
> 2)
> runsp -fc 1
> runsp -min -fc 0.5 -ec 0.0001 -cc 0.001
>


-- 
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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