Lvol from TCHZ's Y and Z

widr

Hello

I would like to calculate lvol, as in LVol_FWHM_CS_G_L, but based on refined Y and Z parameters from the TCHZ peakshape. (If you wonder why, it's part of a Python implementation, let's say "for convenience"...)

So far I seem to understand that

lvol = 1 / voigt_integral_breadth(1/cs_g, 1 / cs_l)

Can I relate Y and Z to cs_g and cs_L? and if so, how?

Thanks

Edit: to be more precise: I fitted all other tchz parameters with a line shape standard while fixing y and z (or z and y?) to 0.

johnsoevans

There's probably no short answer to this that will keep keep everybody happy. My personal take on TCHZ and related functions is that they're convenient mathematical forms that often do a reasonable job of fitting experimental peaks. However there's no physical reason why peaks should obey this form (and many reasons why the may not). You should therefore interpret values with caution. There's a nice new tutorial discussing some of this on the other webpages by Paolo Scardi (https://topas.webspace.durham.ac.uk/tutorial-wppm/).
That said, the various parameters in the TCHZ function can be related to size/strain contributions. There's some detail in the mathematical appendix of the old gsas manual (just google gsas manual). In the version I printed out 30 years ago it's around page 130.
One minor warning: different Rietveld packages swap the X and Y names for the size- and strain-related Lorentzian contributions. I think GSAS and TOPAS have them switched.