[Ifeffit] Problem with Hephaestus at Ca L-edges (Matthew Marcus)

[Bruce Ravel]

On 09/24/2015 03:35 PM, Matthew Marcus wrote:
> 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?

Who knows?  I wrote that bit of code a long time ago.  Whatever the 
reason was that I chose +/-50 eV -- I am sure it was brilliant!

The next release of Demeter will do this much more sensibly, as seen in 
the attached screenshot.

Thanks for bringing this up.

B


>      mam
>
> 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.
>>
>> B
>>
>>
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-- 
  Bruce Ravel  ------------------------------------ bravel at bnl.gov

  National Institute of Standards and Technology
  Synchrotron Science Group at NSLS-II
  Building 535A
  Upton NY, 11973

  Homepage:    http://bruceravel.github.io/home/
  Software:    https://github.com/bruceravel
  Demeter:     http://bruceravel.github.io/demeter/
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