[Ifeffit] charge transfer

Bruce Ravel bravel at bnl.gov
Fri Jan 2 08:30:24 CST 2009

On Friday 02 January 2009 09:15:05 am Bruce Ravel wrote:
>   what does charge transfer mean in FEFF?
>   I cant understand what the number of charge transfer like 0.058, -0.073
>   means.  The number indicate the number of electron in atom?
>   If anybody knows it, please answer
>   Charge transfer:  iph  charge(iph)
>        0    0.058
>        1   -0.073
>        2    0.072


Feff8 does a trick called "self-consistent potentials".  It works like this: 
Feff8 sarts by computing the muffin tin potentials in a many rather similar 
to Feff6.  It then computes the electronic densities of states for a 
reasonable set of low-value angular momentum states (usually up to l=3).  
With those DOS calculation, it integrates in energy to find the energy at 
which the integral of the DOS equals the number of valence electrons in the 
system.  It is likely that each atom has a different number of electrons than 
the free atom.

Now each atom is differently charged than the starting configuration.  The 
muffin tin potentials are recomputed, the DOS is recomputed, and the integral 
is done again.  This process is repeated until the charge on each atom stops 
changing.  That is the sense in which it is self-consistent.

At the end of this self-consistency loop, Feff8 reports the net change in 
charge (in units of number of electrons) on each atom type.  In your case, to 
attain self-consisteny, a small bit of charge is added to the absorber and a 
small bit of charge is taken away from the other two atoms.



 Bruce Ravel  ------------------------------------ bravel at bnl.gov

 National Institute of Standards and Technology
 Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2
 Building 535A
 Upton NY, 11973

 My homepage:    http://xafs.org/BruceRavel
 EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/

More information about the Ifeffit mailing list