[Wien] Force calculations: a problem with Bi

[mazin]

SO is of course physically important, but irrelevant for my question: 
the forces should be consistent with the total energy withing given 
approximation.

There is a problem with describing SOMETHING here, and it may very well 
be the 6s electron. Yet it strikes me as unlikely for two reasons:
(1) Bi is trivalent here, so the 6s is pretty much empty
(2) I find null sensitivity to RKmax, while the 6s state is very diffuse.

Do you have any particular experience of doing something 
not-immediately-obvious with Bi?

Thanks
IM

Rocquefelte wrote

I also looked at systems containing bithmuth atoms some times ago and I
just remember that Bi should be treated with care:
- problem of the description of the 6s lone pair electron
- necessity or not to add spin-orbit to properly describe the effect of
this heavy element on the band structure.

In your case, would it be possible that the problem you have to solve is
related to the difficulty to properly describe the 6s(Bi) lone pair
electrons?