[Ifeffit] Problem with Hephaestus at Ca L-edges (Matthew Marcus)
mamarcus at lbl.gov
Thu Sep 24 14:35:48 CDT 2015
OK. Now I get it. Why use 50eV? Since lifetime and other broadening is not taken into acocunt in any of these tables, why not use a very small number?
On 9/24/2015 11:07 AM, Bruce Ravel wrote:
> On 09/24/2015 01:43 PM, Matthew Marcus wrote:
>> See the attached ppt for the demo. I think this gives the whole
>> repeat-by and interpretation. Am I just missing something? That would
>> not be totally surprising.
> The algorithms in Hephaestus are pretty dim-witted and tuned (such as they are) to getting the calculations more or less right in the hard X-rays. I don't even try to do calculations in the soft x-ray range correctly. For example, the edge step calculations do the calculation at something like +/-50, which is a very stupid choice for soft x-ray energies. That should explain why L2:l3 ratio is 1. Presumably also why the L1 step is negative!
> See, e.g. https://github.com/bruceravel/demeter/blob/master/lib/Demeter/UI/Hephaestus/Formulas.pm#L274
> You cannot trust anything Hephaestus has to say about edge jumps below 3-ish keV. Since the +/-50 is hard wired in, the jump ratios will be nonsense for any element for which the energy difference between the L2 and L3 edges is less than 100 eV.
> The Delta mu/rho numbers that you cite are interpolated from the Elam (usually) tables and should reliable to whatever extent you consider the table reliable.
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