Hi John,
Thus we have attempted to use the theoretical mu_0 from FEFF as an a priori, and spline corrections on top of that. Thus the form of mu_0 would be:
mu_0 = mu^thy_0(E,E_0,Gamma)[1 + lambda(E)]
where the theoretical mu^thy_0 has an adjustable edge position (E_0) and broadening (Gamma), and lambda(E) is the spline correction which includes both instrumental variations with E and theoretical errors.
In our experience, the FEFF8 mu^thy_0 can often give a good approximation to mu_0, even near the edge where there are large white lines.
That sounds interesting. But if you include a spline with the calculated mu0(E), how important is the mu^thy_0(E)? Like, how much work do you need to put into mu^thy_0 if you have lambda to pick up the slack? On the one hand, since a spline is needed, it might imply that you don't really gain much. On the other hand, it might also imply that you could calculate and tabulate a reasonable 'universal background function' for any given absorber-scatterern pair as a starting background curve. Otherwise, it seems to me that the prior information that goes into getting mu0(E) might be roughly equivalent to using Feff to generate a standard chi(k) for autobk.
We'd be interested in comments/suggestions on this approach. For example, how best to represent small corrections to the broadened edge step (e.g., arctangent corrections).
I think the experimental broadening should be adjustable, probably defaulting to a Lorenztian with Delta E/E = 1.e-4. Anyway, I'd be interested in comparisons of this with autobk with/without a standard chi(k). And, of course, code donations for improved algorithms are always welcome. ;). --Matt