[Ifeffit] Core-hole Lifetimes in Hephaestus 0.9.26

Mon Sep 28 14:14:23 CDT 2020

Hi Matt,

Well, independent of what Krause et al. have done, the correct uncertainty
relation between core-hole widths as FWHM (full width at half maximum) and
the lifetime is

lifetime = h_bar / FWHM

from the corresponding half-width (HWHM) expression

HWHM x lifetime >= h_bar / 2

Again, I just stumbled upon this when using Hephaestus, and the lifetimes
were all oddly "long".
The above relations are often garbled up due a HWHM-FWHM mix-up (the HWHM
being the "spread" of the Cauchy/Lorentz/Breit-Wigner distribution towards
higher and lower energy around the center etc.) as well, giving factor of
two errors...

Anyway, thanks for taking the time to look into this!

Cheers,

Daniel

> Hi,
>
> Ah, Krause et al *do* use hbar, not h, so yeah With gamma = 0.2 eV, and h
> ~= 4.13567e-15 eVs (hbar ~ 6.582e-16 eVs), then lifetime is ~3 fs.
>
> That is probably the mistake that hephaestus is making too.  FWIW, we are
> not currently, but could be reporting core-level widths and lifetimes at
> https://xraydb.xrayabsorption.org/
>
>
> On Mon, Sep 28, 2020 at 1:37 PM Matt Newville <newville at cars.uchicago.edu>
> wrote:
>
>> I believe it is using (or intends to use)
>>
>>     lifetime = hbar /gamma
>>
>> which is what Krause et al give.  With gamma = 0.2 eV, and hbar ~=
>> 4.13567e-15 eVs, then lifetime is ~20fs.
>> Maybe I'm missing something more subtle?  FWIW, these reported numbers
>> for
>> gamma in eV are described by Krause et al as "FWHM".
>>
>> --Matt
>>
>>
>> On Mon, Sep 28, 2020 at 1:13 PM Daniel Przyrembel <
>> daniel.przyrembel at fu-berlin.de> wrote:
>>
>>> Hi Matt,
>>>
>>> Thanks for the quick reply!
>>> However, I seem to not have made clear my concern...
>>>
>>> The widths in energy (eV) are fine.
>>>
>>> However, in "Hephaestus", the "souped-up periodic table for the X-ray
>>> absorption spectroscopist", these level widths in energy (eV) are also
>>> given as equivalent lifetimes (in fs), however incorrectly: A level
>>> width
>>> of ~0.2 eV in fact corresponds to a lifetime of ca. 3 fs, not ~30 fs as
>>> given there.
>>>
>>> Those lifetimes shown in Hephaestus all seem to be off by a general
>>> factor
>>> of 10. I guess that is just the energy width/lifetime conversion gone
>>> slightly wrong...
>>> I imagine I'm not the only one using Hephaestus as a convenient tool to
>>> look stuff up quickly, so I thought it might be useful to point out
>>> this
>>> flaw.
>>>
>>> Just to make sure, I have again imported the xraydb: That has not
>>> changed
>>> Hephaestus' behavior in terms of the lifetime info (I'm using the
>>> latest
>>> 64-bit version on Windows).
>>>
>>>
>>> > Hi Daniel,
>>> >
>>> > Thanks - that does seem wrong.  FWIW, Larch uses XrayDB which uses
>>> > corehole
>>> > widths from Krause and Oliver for Z>10 and Keski-Rahkoken nand Krause
>>> for
>>> > Z<10.
>>> > For the F K edge, this give 0.2089 eV.  For this or other core-hole
>>> > widths,
>>> > and assuming you have Python installed, try:
>>> >
>>> >   ~> pip install xraydb
>>> >   ~> python
>>> >   >>> import xraydb
>>> >   >>> xraydb.core_width('F', 'K')
>>> >   0.2089
>>> >
>>> > Or install Larch and use
>>> >
>>> >    ~> larch
>>> >    larch> core_width('F', 'K')
>>> >    0.2089
>>> >
>>> >
>>> >
>>> > On Mon, Sep 28, 2020 at 12:08 PM Daniel Przyrembel <
>>> > daniel.przyrembel at fu-berlin.de> wrote:
>>> >
>>> >> To Whom it may concern,
>>> >>
>>> >> I am quite sure there is a general lifetime/energy-width conversion
>>> >> error
>>> >> in Hephaestus: All core-hole lifetimes seem to come out too long by
>>> a
>>> >> factor of - as it seems exactly - 10:
>>> >> E.g. the lifetime of the F K-edge with a width of 0.25 eV is given
>>> as
>>> >> 25.30 fs instead of ca. 2.6 fs (width = h_bar / lifetime).
>>> >>
>>> >> This glitch was present in 0.9.25 already and, as I noticed after
>>> >> updating, prevails in 0.9.26. I have not tried earlier versions.
>>> >>
>>> >> Best regards,
>>> >>
>>> >> Daniel
>>> >>
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>>
>>
>> --
>> --Matt Newville <newville at cars.uchicago.edu> 630-252-0431
>>
>
>
> --
> --Matt Newville <newville at cars.uchicago.edu> 630-252-0431
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