sratio range ?

[Clara Doisneau]

Hello everyone,

I am doing a fit of a tunsgten oxide and my best fit is with a sratio value of 0.5 or even lower. So I was wondering if there is a range of values for sratio ? Is 0.5 to low ? 

Even if it works from a mathematical point of vue, is there a real scientific meaning for such low value ? 

I have never found an answer in any paper or books. 

Thank you in advance ,

Clara 

PhD student in chemistry lab in France (LCMCP,  Sorbonne Université)

[Simon Billinge]

Dear Clara,

It is a little difficult to say for sure with the information you shared, but in covalent materials where we sometimes use SRAT (actually, we don't use it that frequently, preferring instead delta2 or delta1) can show values of SRAT similar to what you describe.  It also depends on where you set your RCUT.

For the oxide that you are studying , my recommendation is probably to not use SRAT/RCUT but use delta1 OR delta2, whichever works better.

S

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Simon Billinge

Professor, 

Department of Applied Physics and Applied Mathematics

Columbia University

[Clara Doisneau]

Thank you very much Dr Bilinge for your (quick !) answer

We are working on a WO3.H2O material  actually, and we have a sratio of 0.5 and a rcut of 4.0, to refine better the first peak of W-O, and above all the second peak which corresponds to the first W-W connectivity by 
edge. We were fitting with delta2 (with a value around 1 or 2) also, but  it is really the sratio that allows us to fit correctly the W-W peak. Is it not possible to do both sratio/rcut and delta2 at the same time ? It seems that it should not work together correctly, but in our case it works quite well, and all the other parameters refined have coherent values scientificcally speaking. 

Thank you again for your answer ! 

Clara