[Ifeffit] Exploring XANES data for getting EXAFS results

Matt Newville newville at cars.uchicago.edu
Fri Jan 16 09:53:16 CST 2015


On Fri, Jan 16, 2015 at 9:21 AM, Marcelo Alves <mealves at gmail.com> wrote:

> Hi all,
>
> I wonder if it is possible from XANES unusual data treatment to get
> information such as number and distances of neigbhors in the first and
> second shells.
>
>
There is an old-ish (like, from the 1950's I think) and fairly heuristic
rule that the XANES edge energy shifts scale as 1/R^2 for the nearest
neighbor.    I think that Grant Bunker has a nice set of slides showing
this, somewhere on the web.  For example, I think this explains well slight
energy shifts in the peak energy of the sulfate resonance.     My
recollection is that it works pretty well for many well-constrained set of
spectra, but isn't quite as quantitative and readily applicable to unknown
systems as one might hope.

It's also sort of related to the idea of bond-valence that, for a given
class of systems (say, oxides of a particular metal), R, N, and formal
valence state are not independent quantities.

--Matt
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