Hi Patricia,
When you say "worse than the initial one," what do you mean? If it's a "worse" match than nonsensical fit results, but makes some physical and chemical sense, I'd personally argue it's a much better fit ;) What you are doing seems reasonable to me, but I would further recommend keeping your fit component selection as simple as possible. I'm a big proponent of two-component fits, maybe three if there's a really good reason. I feel like a lot of people do multicomponent (3-4 fitting spectra, maybe even more) LCF with the argument that the inclusion of additional components improves the fit statistics...But to me that gives a false sense of certainty that the technique doesn't really allow (at least for the systems I work with). For reporting qualitative trends, it seems like you're on the right track. Perhaps unless it's a qualitative trend of a minor component that might not even be there at all and you're basing your entire argument on it definitely being there, which uhh. Seems to happen a lot. Cheers, Mike > On Mar 11, 2021, at 1:42 AM, Patricia Poths <patriciapo...@chem.ucla.edu> > wrote: > > > Hi, > > I am a theoretical chemistry PhD student working on fitting experimental > spectra with computed spectra in order to get a better understanding of the > composition. In the LCF process with athena, I have found that when I allow > "sum coefficients to 1", I get an unphysical negative coefficient of the last > standard- after reading through the mailing list I understood why, and so no > longer use that. The sum of my coefficients during the fitting now is close > to 1- generally within the range of 0.95-1.1 at the absolute extremes, but > more often around ~0.98- ~1.05. > > In order to compare these coefficients, I renormalize them to 1, so they can > represent the fractions of each component present. However, to test this I > took the new normalized coefficients and summed up the standards with their > respective weights to create this normalized "fit", and found that it is > worse than the initial one. Is this something I should be concerned about > when reporting the qualitative trends in how the composition changes? And if > so, is there a better way to do the fits in a more normalized way? > > Many thanks, > Patricia > _______________________________________________ > Ifeffit mailing list > Ifeffit@millenia.cars.aps.anl.gov > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit > Unsubscribe: http://millenia.cars.aps.anl.gov/mailman/options/ifeffit _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit Unsubscribe: http://millenia.cars.aps.anl.gov/mailman/options/ifeffit
