[Wien] Force calculations: a problem with Bi

[Stefaan Cottenier]

Two simple things to check first (maybe too simple):

* Do you have FOR (instead of TOT) in case.in2(c) in the last  
iteration? Otherwise Pulay corrections are not taken into account, and  
that might explain your observations.

* Do you use spin-orbit coupling? Forces in wien2k are not consistent  
with spin-orbit.

Stefaan


Citeren mazin <mazin at nrl.navy.mil>:

> I am calculating a Bi-containing compound, BiOCuS. It has a rather  
> simple tetragonal structure with two free parameters, Bi (z) and S  
> (z).
>
> When I vary Bi(z) keeping everything else fixed I obtain a well  
> defined total energy minimum at one z, and a well defined Bu force  
> zero at another z. Both sets of calculations are well converged,  
> k-mesh convergence, RKmax, GKmax, fft, linearization parameters, rMT  
> dependences etc are all tested. Including more semicores states does  
> not affect the results either. A closer inspection shows that the  
> force obtain by taking the derivative of the total energy agrees  
> well with the calculated forces, if the latter are shifted by 63  
> mRy/bohr (a huge number). The calculations are nonmagnetic and  
> scalar relativistic.
>
> I vaguely remember having some problems quite some time ago with  
> force calculations for another Bi compound, but at that time I never  
> got to the bottom of that.
>
> I wonder if this is a known problem and if anybody stumbled upon it before.
>
> I.M.
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-- 
Stefaan Cottenier
Center for Molecular Modeling (CMM)
Ghent University
Technologiepark 903 (2nd floor)
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Belgium

http://molmod.Ugent.be
email: Stefaan.Cottenier /at/ UGent.be