[Wien] how to calculate EFG values

[Stefaan Cottenier]

> I want to calculate EFG to correlate with experimental observations. But I
> have never obtain the correct results as the EFG values are quite
> different for the identical Fe atoms in my structure. Do you have advices
> what I need to specify to get correct EFG values. Thanks!

(smile) -- Such a general question can trigger only a very general answer:

First thing to consider: would any bad genius out there program wien2k 
in such a way that you usually would obtain bad EFG values? I guess no. 
If you do the calculation technically right, you get the correct EFG at 
the applied level of theory (probably LDA/GGA).

If that EFG-value doesn't agree with experiment, there can be several 
reasons -- varying from trivial to deep:

* trivial: you made a unit conversion mistake between experiment and wien2k

* less trivial: experiment is right and wien2k is right, but they look 
at different cases -- the atom configuration for which you calculate the 
EFG (and which you expect is the one that appears in Nature) isn't 
exactly the one that appears in Nature.

* deep: perhaps the chosen level of theory is not the appropriate one 
for your particular material.

Stefaan