[Ifeffit] question about sigma2 and atomic distance

[Robert Gordon]

I imagine they could, yes. Motivation to do so is another question entirely.

Considering myself more of an experienced amateur, and a fan of the
Socratic Method, let me ask you a few questions:

What do you currently understand about the relationship between two atoms
in a material and the mean square relative displacement
(i.e. sigma^2) associated with the distance between them?
What does it mean to have a mean-square-displacement? ..and then a
mean-square-relative displacement?
How would correlated, anti-correlated and uncorrelated relative motion
affect the msrd?

Now extend this thinking to an ensemble of atoms.
What might you expect to be the source of a msrd in a perfect crystal at
finite temperature?
What additional contribution may result from imperfections?








On Wed, Jun 7, 2017 at 7:12 PM, Shaofeng Wang <wangshaofeng at iae.ac.cn>
wrote:

> Dear everyone,
>
> Could experts explain the relationship between sigma2 and atomic distance
> of same two atoms?
>
>
> Best regards,
>
> Shaofeng
>
> --------------------------------------
> Shaofeng Wang, Ph.D of Geochemistry
> Environmental Molecular Science Group
> Institute of Applied Ecology, Chinese Academy of Sciences
> Shenyang, 110016, China
> wangshaofeng at iae.ac.cn
> www.iae.cas.cn
>
>
> *From:* Shaofeng Wang <wangshaofeng at iae.ac.cn>
> *Sent:* Friday, June 02, 2017 4:32 PM
> *To:* XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
> *Subject:* [Ifeffit] a question about S02
>
> Hi everyone,
>
> I am fitting a standard material scorodite. The fitting results are pretty
> good, but the S02 is around 1.2 when the k range = 4-13.5. Is this result
> reasonable? Please see the attached files.
>
>
>
> Best regards,
>
> Shaofeng
>
> --------------------------------------
> Shaofeng Wang, Ph.D of Geochemistry
> Environmental Molecular Science Group
> Institute of Applied Ecology, Chinese Academy of Sciences
> Shenyang, 110016, China
> wangshaofeng at iae.ac.cn
> www.iae.cas.cn
>
> ------------------------------
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