Re: Feff Calculations on Charged (Non-neutral) Compounds

["John J. Rehr" <jjr@leonardo.phys.washington.edu>]

Hi Jeff and others interested in getting charge transfer with FEFF.
> 
> I have a question about FEFF calculations on charged clusters. I guess 
> the root of the question is how do I add or remove electrons  to give 
> the cluster a net charge?

  Charge transfer simply changes the fermi level, since the fermi
energy is determined by the total number of filled states.

  Thus the correct way to do calculations for charged clusters is to
shift E_F by varying Vr in the EXCHANGE card.  To get the charge transfer,
one can use the expression

delta N = delta N/ deltaE * delta E = (total-DOS) * Vr

You need to run LDOS, of course, if you want delta N precisely.
Alternatively you might use a free electron estimate of the total DOS.
Otherwise, simply vary Vr to fit the data. FEFF does have an ION card
which was coded to do this, but we're not sure it can be trusted with FEFF8. 

 Cheers,
  John Rehr