[Ifeffit] Problem with large so2

Scott Calvin dr.scott.calvin at gmail.com
Tue Jan 3 09:59:18 CST 2017

Hi Raj,

I haven’t looked at your files, but the kinds of results you are describing often indicate the model you are using beyond the first shell is incorrect. It may be that it has the wrong elements (e.g., heavier elements are present than what you modelled) or that the model includes split distances when in reality the compound is more symmetric. 

In short, no, the high second S02 does not make sense (although it would be good to know the uncertainties). 

Scott Calvin
Lehman College of the City University of New York

> On Jan 3, 2017, at 9:38 AM, Raj kumar <rajrk37 at gmail.com> wrote:
> Dear All,
> I have been trying to fit EXAFS signal of YbVO4 both in bulk and nanoparticles form. Here, I would like to estimate so2 from bulk (reference) and subsequently use the number, as normalization parameter, to calculate the co-ordination number in all nanoparticles. Nanoparticles were synthesized by solution route. From our earlier understanding on the synthesis, in some cases, Yb may or may not completely involve in reaction. Therefore, I except Yb in two environments, one surrounded by mere oxygen (in precise oxygen-Hydrogen; due to disorder one may expect a single peak) and another one in YbVO4 environment. With this info and for reasonable fit, I have used two so2 as free parameters for N: one for first shell (oxygen at two distances) and another for rest other shells.  If I use single so2, I obtain the value of around 0.92 with unsatisfactory fit whereas the fit seems plausible with two so2 i.e., 0.75 and 2.2, respectively. Using the same strategy, I could successfully fit the nanoparticles again with large second so2 (1.79). From literature and IFEFFIT earlier discussion, i understood that so2 should be between 0.8-1.2 value. Here, I would like to know, does this huge second so2 value makes sense? is the obtained so2 value can be used to calculated coordination number for unknown? Further, i have attached my worked files with this message.
> Regards,
> Raj
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