[Wien] Fermi-contact hyperfine fields

[Peter Blaha]

Hi,

No, Fermi-contact term has not "improved", we are still using the same 
GGA approximation.

However, in bcc Fe (a ferromagnet) the situation is usually VERY 
different from a NMR calculation.

In bcc Fe the main contribution comes from the core electrons (3s), 
which respond to the huge 3d moment and the hyperfine field is 30 T 
!!!!. The localized core electrons are not well describe by GGA.


In NMR for paramagnetic metals, often (not always) the main contribution 
comes from an reoccupation of the valence 4s (or 5s in 4d elements, ...) 
and this valence electrons are "hopefully" well described by GGA.

It is true, however, that sometimes the 3d DOS at EF is large, which 
introduces a 3d moment and also some sizable core response to the HFF. 
However, the fields are only ppm of 100T, so much much smaller.
(PS: we know for instance that the shift in hcp Sc is completely wrong 
in DFT calculations, because GGA seems to overestimate magnetism).

Peter


Am 21.09.2017 um 13:37 schrieb pieper:
> Dear Wien2k users,
> 
> I have a question about the Fermi-contact fields printed at the HFFnnn 
> labels in the scf file.
> 
> Back in 2010 Peter Blaha advised in this mailing list that the 
> Fermi-contact interaction can be underestimated at least for 3d-metals 
> like Fe by 10 - 20%
> [www.mail-archive.com/wien at zeus.theochem.tuwien.ac.at/msg02201.html] and 
> Pavel Novak indicated that in his opinion it might be difficult to 
> correct this misbehaviour by some suitable local or semi-local Vxc 
> [www.mail-archive.com/wien at zeus.theochem.tuwien.ac.at/msg03011.html].
> 
> Since this was pre-NMR-package and at the beginning of hybrids I wonder 
> wether the situation has improved in the meantime? The NMR-package as I 
> understand it calculates shielding current distributions so I don't 
> expect it improves on Fermi-contact fields - is that correct? And is 
> there a way to get improved values from hybrids that I am unaware of?
> 
> Best regards,
> 
> Martin Pieper
> 
> 

-- 
Peter Blaha
Inst.Materials Chemistry
TU Vienna
Getreidemarkt 9
A-1060 Vienna
Austria
+43-1-5880115671