Re: [Ifeffit] Use of the 3rd and 4th Parameter

2014-06-16 Thread Scott Calvin
Hi Michael, It is best to start by guessing the third cumulant only, leaving the fourth cumulant set to zero. A survey of the published literature shows very few examples where the fourth cumulant has been fit--by that point the cumulant expansion itself is starting to become iffy, which is not

Re: [Ifeffit] Use of the 3rd and 4th Parameter

2014-06-16 Thread Matt Newville
Michael, The values for C3 and C4 should be very small -- they are in Ang^3 and Ang^4, and should be numerically smaller than sigma2 (in Ang^2). I would expect values of 0.001 for C3 in a highly disordered system. I'm not sure anyone has actually seen a value for C4 that was not consistent wit

[Ifeffit] Use of the 3rd and 4th Parameter

2014-06-16 Thread Michael Kömm
Hello, I'm trying to make an EXAFS analysis on the Structure of Tb in a borogermanate glass System. The reference is an .cif of Terbium-Gallium-Garnet (TGG). I expect some disorder caused to working in glass. Therefore I would like to use the 3rd and/or the 4th parameter. I tried to set a gu

Re: [Ifeffit] Scattering paths in XANES calculations

2014-06-16 Thread Bruce Ravel
On 06/16/2014 09:20 AM, Stefanie Roese wrote: Ah okay. I think now I get it. Is it correct that in the mu(E) spectrum you plot the total spectrum in blue and in red you chose different fms-radii like 2.5, 3.0, 4.1 to get the XANES spectrum for different shells? Yes. B Or are the red curves a

Re: [Ifeffit] Scattering paths in XANES calculations

2014-06-16 Thread Stefanie Roese
Ah okay. I think now I get it. Is it correct that in the mu(E) spectrum you plot the total spectrum in blue and in red you chose different fms-radii like 2.5, 3.0, 4.1 to get the XANES spectrum for different shells? Or are the red curves another varied FEFF parameter? Thanks so much for your suppo

Re: [Ifeffit] Scattering paths in XANES calculations

2014-06-16 Thread Bruce Ravel
On 06/16/2014 03:43 AM, Stefanie Roese wrote: thanks for your answer! My problem is how to get the E/mu information for each single scattering path. Sorry, Stefanie. I don't know what that means. Feff computes mu(E) on a cluster and chi(k) on an individual path. In my talk, I plot mu(E) on

Re: [Ifeffit] Scattering paths in XANES calculations

2014-06-16 Thread Stefanie Roese
Dear Bruce, thanks for your answer! My problem is how to get the E/mu information for each single scattering path. If I get it right, the xmu.dat contains the sum of all scattering paths. This is the blue curve in your talk. But there are also the spetra for the first,s econd, third,... path at pag