[Ifeffit] EXAFS

[Francisco Garcia]

Dear all,

I tried computing K-edge chi(k) for a solvated metal ion. For each
snapshot, I simply carved out a cluster of radius 6 Ang around the
metal.

1. if I set RMAX to say 5.5 in feff.inp, the chi(k) plot looks totally
different from the case where the RMAX line is commented out
(particularly k>10). I thought RMAX is the largest metal-H or metal-O
separation but I think I am wrong

2. I dont quite understand why the number of paths increases
(sometimes by a factor of 3) when I set RMAX as opposed to the case
where I comment it out.

3. From time to time I get warnings indicating that a water O-H
distance is too short:

   WARNING:  TWO ATOMS VERY CLOSE TOGETHER.  CHECK INPUT.
    atoms     5    7
     5    0.14400    2.09700    1.16300
     7    0.77400    2.67400    1.00800

I tried setting FOLP to 0.8 for H but the warnings persist.

4. On what criteria are sigma2 and s02 chosen? They are not usually
reported in published theoretical papers and I was wondering if they
are arbitrary.

5. Finally, is the chi(k) dependent of which version of FEFF is being
used. I am asking this because the peak height of my FEFF6 chi(k) is
slightly lower than that of published results using FEFF8.

Thanks