For EXAFS and EXAFS fitting, the FMS and XANES calculations should not be done. For EXAFS, these values don't matter (I think!). For what it's worth, L_fms basically sets how high in k the FMS approach works well enough to use. It's typically a number <~ 5. I'm not sure what l_scmt is...
I agree that the FMS and XANES calculations need not be done if you are interested in doing EXAFS analysis.
(i.e. in the past I have used the following for 2 Au's in the surface) POTENTIALS * ipot z element l_scmt l_fms stoichiometry 0 79 Au 3 3 0.001 1 28 Ni 2 2 4 2 79 Au2 3 3 4
Oh, I think those might be ipot z element lmin lmax
and that lmin=-1, lmax=3 are reasonable default values. Hopefully someone can clarify this....
That's not correct. "scmt" = "self consistent muffin tin" and "fms" = "full multiple scattering". Elsewhere in the feff-iverse, scmt is referred to as "scf" or self-consistent field. The l_scmt value is used in the calculation of the self-consistent potentials. The l_fms value is used in the calculation of the final densities of state and xanes. Each one limits the size of the angular momentum potion of the basis used in the matrix algebra required to do the feff8 calculation. The reason there are two is to allow the possibility of considering different sized bases while determining the potentials than while computing the final xanes spectrum. There are some reasons why one might want that freedom. In practice, one can usually use the same values for l_scmt and l_fms. For first row elements, l=1 is often fine. If one has the time and computer power, l=2 might result in a better calculation. For transition metals, l=2 is a good choice. For heavier things, l=3 should be used. Heavier elements are likely to have f-electrons in the valence band or low-lying f-states, thus a value of 3 is necessary. An l-value of -1 tells feff to use its default for that element. The defaults are more-or-less as I explained in the last paragraph. Thus, the easiest way to use feff8 is to use l=-1 for every atom and for both scmt and fms. B