Re: [Ifeffit] Core-hole Lifetimes in Hephaestus 0.9.26

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 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@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@fu-berlin.de> wrote:

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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

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