[Ifeffit] charge transfer

Scott Calvin SCalvin at slc.edu
Fri Jan 2 10:19:29 CST 2009


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
>
> -- 



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