Dear Harry,
To a good approximation, using a decreased lifetime broadening works for simulating HERFD-XANES. See
https://doi.org/10.1021/jp063416t where conventional and HERFD XANES are calculated with FEFF by decreasing the broadening (Fig. 2). This is done in the EXCHANGE card, e.g. to decrease the HWHM by 1.5 eV, apply on the 3rd number:
EXCHANGE 0 0.0 -1.5 -1
To use the default tabulated Pt L3 broadening (about 5 eV), use 0 (EXCHANGE 0 0.0 0 -1 )
Note: experimentally this is not entirely accurate, because in HERFD you select the Pt L-alpha1 line, while in TFY you integrate over ~300 eV of this line, taking all other transitions as well. For a detailed explanation see
https://doi.org/10.1016/j.cattod.2008.11.019 (Fig 2). But it should represent the results pretty well.
Also note that specifically for Pt L3, the best match of the simulated white line with experiment is obtained by ignoring the core-hole (assuming its full screening), by applying the COREHOLE NONE card option. If this is not done (COREHOLE FSR or RPA is used), the white line intensity is strongly under-estimated, at least in Pt metal. See
https://doi.org/10.1023/A:1013849814153 for example and explanation.
Best regards,
Alexey