[Wien] A way to evaluate if minimization without SO is correct ?

[Laurence Marks]

Two alternatives:

a) For directions where you do not have inversion symmetry, the sum of the
forces with a well converged calculation should be zero. You can use this
to estimate from the force of the light atoms what those on the heavy atoms
have to be.

b) Using clmextrapol (which is very efficient), calculate the forces by
applying small displacements (finite differences).

A third option is to add a non-derivative optimizer to PORT, but this would
require some real work.

On Tue, Dec 4, 2018 at 9:41 AM Luc Fruchter <luc.fruchter at u-psud.fr> wrote:

> It has been said many times that forces are not correct when spin-orbit
> is included.
> Also, that the contribution of SO should generally be small, compared to
> energies that determine the equilibrium positions, so that minimization
> without SO should be a good approximation, for most cases.
>
> I wonder, however, if the following scheme may help to get confidence
> that a minimization without SO indeed provides a structure close to
> equilibrium:
>
> - perform minimization without SO,
>
> - switch-on SO on heavy atoms of the equilibrated structure,
>
> - fix these atoms, and relax the structure for the light atoms (like
> Oxygen)
>
> - check if this relaxed structure is close to the one obtained at the
> first step.
>
>
> Does this sound reasonable ?
>
>
> Thanks
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-- 
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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