Adding to my previous example of the feff.inp file that calculates single scattering paths only, below are the links to FEFF6 document where the use of SS and OVERLAP cards is explained. As I checked some time ago, without the OVERLAP card, the results may be different (and worse) than with it, so it is more safe to use this card. As reality checks have shown, It produces very similar results for single scattering feffxxxx.dat paths (if the feff.inp file is constructed correctly!) to those calculated when the atoms list is explicitely used to model the structure.
 
 http://leonardo.phys.washington.edu/feff/Docs/feff/feff6-4.html#ss
 
http://leonardo.phys.washington.edu/feff/Docs/feff/feff6-4.html#ove
 
Anatoly
 
Anatoly Frenkel
Yeshiva University