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

[Peter Blaha]

Yes, this is the best way you can do.

In that way you even get the "indirect" spin-orbit effect on the light 
elements correct and often one can hope, that when the forces on all 
other atoms are small, also the force on the single heavy element will 
be small.

If there is only one heavy element and it is maybe even at a position 
with only one free parameter ?, this can be optimized using E-tot alone, 
by manually moving this atom a bit, then constrain it and optimize the 
others, and compare E-tot. But it might be numerically quite noisy ... 
and becomes impossible for more heavy atoms, ....



On 12/4/18 4:41 PM, Luc Fruchter 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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-- 

                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
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