[Ifeffit] can sigma square ever be less than zero?

Chris Patridge patridge at buffalo.edu
Mon Jun 28 15:10:12 CDT 2010

Hello all,

I am working on W L3 edge data.  W is acting as a substitution dopant in 
vanadium dioxide at rather low concentration.  In a past mailing 
conversation discussing Feff6 overestimation of E0 for heavier elements 
it was mentioned that the E0 could be past the rising edge due to the 
white line from W data.  Well using this comment I aligned data using 
the theory method well explained by Shelly Kelly SnO2 example.  
Literature suggests W approximates WO2 cubic structure locally instead 
of the VO2 unit structure.  Then fitting the first oxygen coordination 
shell paths which are well isolated from the other paths, it gives 
reasonable values for amplitude and enot of 0.77 (0.17) and -1.14 (3.06) 
respectively.  delr is -0.067 (0.028) and then ss comes out to -0.00036 
(0.00414).  Can ss be negative if the uncertainty brings it above 0?

Thank you all,

Chris Patridge
PhD Candidate
Department of Chemistry NSC 405
SUNY Buffalo

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