[Wien] new optimization scheme

[Peter Blaha]

If you have inversion symmetry, then   :FSUM should always be exactly zero,
even when you have only partial (or wrong) forces.

If you do not inversion, :FSUM should still be zero, but due to non-scf conditions
or other problems with basis sets,... it might not be the case.
The  whole set of atoms could then "accelerate" and move freely through your unit
cell (at least in one direction; since symmetry does not change in such cases).
Fixing ONE atom would then avoid such movements.

Am 03.06.2011 13:06, schrieb Lyudmila V. Dobysheva:
> Thank you, dear Laurence and Peter.
>
>> In the case you gave there is nothing fixing the origin naturally
>> along the z axis (I suspect).
>
> Yes, and the cell really seems to move freely during the process. I see which
> atom to pin.
>
> Do I understand correctly:
> If there exists a force in :FSUM (:FCHECK), it means that we should pin the
> cell in this direction.
> The line "Note: symmetry trapping" means only absence of inversion.
>
> Best regards
>    Lyudmila Dobysheva
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-- 

                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-15671             FAX: +43-1-58801-15698
Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
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