I'd add to Bruce's explanation that the numbers usually end up being qualitatively similar to what you'd expect from oxidation states, but much smaller than the oxidation number. Saying iron is in a +2 oxidation state, for instance, doesn't really mean two electrons have been completely transferred from the iron atom to the ligands. You'll generally see FEFF come up with a much smaller positive number than +2 for iron in that case, but it will still recognize that the iron is positive. And although I haven't paid close attention to this, I'd expect in a system with mixed +2 and +3, that FEFF would probably assign a bigger charge transfer to the +3 in most cases. --Scott Calvin Sarah Lawrence College On Jan 2, 2009, at 6:30 AM, Bruce Ravel wrote:
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
Jeong,
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.
B
--