I have one technical questions on EELS calculation.
A calculated EELS spectrum is smeared/broaden so that one compares it with experimental results.
I understand three kinds of broadening are known in EELS (referring to Unoccupied Electronic States, Fundamentals for XANES, EELS, IPS and BIS, Textbook, 1992)
1). instrumental broadening, which is expressed in Gaussian function with FWHM determined by the device
2). core-hole lifetime broadening, which is probably hundled with Lorentzian smearing scheme
3). excited-state lifetime broadening, which requires certain energy-dependent broadening
I found the comments in XAS tutorial like
“The broadening of the core electron absorption spectrum is controlled by the tag CH_SIGMA. Usually it is good practice to set this value low and broaden the spectrum in post processing.”
“Another important issue is the broadening. Because the observed broadening is driven by many factors depending on the particular experimental setup, ....”
Does CH_SIGMA correspond to No.2) ?
If I’d like to apply No.1), Should I use SIGMA in VASP tag?
Is No.3) implemented in VASP? how can I control it?
I may have missed some descriptions, but I would appreciate your comments.
Best regards,Tomohisa Ogawa