Order of the approximation used in module genfmt. FEFF uses
order 2 by default, which is correct to terms of order ,
and corresponds to 6x6 scattering matrices in the Rehr-Albers
formalism. Single scattering is calculated exactly to this order.
The 6x6 approximation is accurate to within a few percent in every
case we have tried (that is, higher order doesn't change the result
more than a few percent). However
higher shells may require increased iorder for coupling the matrix
elements. Changing the default values requires some familiarity
with the Rehr-Albers paper and the structure of the module genfmt.
To do so, follow the instructions in the FEFF source code in
subroutine setlam. The key iord is passed to
setlam for processing. You may need to change the code
parameter lamtot if you want to do higher order
calculations. For details of the algorithm used by genfmt, see the
paper by J.J. Rehr and R.C. Albers
. For the
and higher edges, you may receive an error
message like: Lambda array overfilled. In that case the
calculations should be repeated with IORDER -70202 (10x10 matrices).
* change iorder for M4 calculations