The construction of the interstitial potential and density may be changed by using this card. .

`ipot`-

potential index.`ipot`defines how to find the interstitial potential.`ipot`=0 (default): the interstitial potential is found by averaging over the entire extended cluster in ``feff.inp`'.`ipot`=1 : the interstitial potential is found locally around the absorbing atom. `irav`-

also changes how the interstitial potential is found.`irav`=0 (default): the equation for V is constructed at`rav`=`rnrm`.`irav`=1 : at`rav`=(`rmt`+`rnrm`)/2.`irav`=2 : at rav=rmt, where`rmt`is the muffin-tin radius and rnrm is the Norman radius. irmt apparently does not exist in the code `irmt`-
`irmt`=0 (default): Norman prescription for mt radii.`irmt`=1 : Matching point prescription for mt radii (do not use). `vtot`-

the volume per atom normalized by`ratmin`(`vtot`=(volume per atom)/`ratmin`), where`ratmin`is the shortest bond for the absorbing atom. This quantity defines the total volume (needed to calculate the interstitial density) of the extended cluster specified in ``feff.inp`'. If`vtot`0 then the total volume is calculated as a sum of Norman sphere volumes. Otherwise, total volume =`nat`(`vtot``ratmin`), where`nat`is the number of atoms in an extended cluster. Thus`vtot`=1.0 is appropriate for cubic structures, such as NaCl. The INTERSTITIAL card may be useful for open systems (e.g. those which have ZnS structure).

* improve interstitial density for ZnS structures. * vtot = (unit_cell_volume/number_of_atoms_in_unit_cell)/ratmin**3)=1.54 INTERSTITIAL 0 1.54