On Sunday 21 February 2010, 07:04:05 am, Neetu parsai wrote:

Hi all, I am searching for the values of mean free path and Debye waller factor of transition metals. Is there any citation available on these values? I want to understand how these are calculated.

Feff uses the values for mean free path from K. Rahkonen and K. Krause, Atomic Data and Nuclear Data Tables, Vol 14, Number 2, 1974. (It is easier to just dig through the Feff source code for the actual numbers that it is to try to find a copy of that paper.) Feff also uses a relatively simple plasmon-pole model to compute other sources of loss. Note, though, that mean free path and other forms of loss are quite hard to distinguish in an EXAFS analysis. Sorini et al, Phys. Rev. B 74, 165111 is a much more modern take on the issue, although their many-pole approach has not yet found its way into common use in Ifeffit and friends. As for sigma^2 values -- the notion of "standard values" is not really very meaningful. sigma^2 depends on coordination environment, bonding strength, temperature, pressure, and probably other things as well. In practice, it is rather difficult to distinguish between mean square variation in bond length arising from thermal fluctuations and from structural disorder. Although there are a few examples in the literature of ab initio calculations of sigma^2 values, in practice sigma^2 is something we measure in an EXAFS experiment, rather than something we take as prior knowledge. That said, sigma^2 values tend to be of the order of 10^(-3) to 10^(-2) in units of Angstrom^2 as used in the formulation of the EXAFS equation implemented in Ifeffit. B -- Bruce Ravel ------------------------------------ bravel@bnl.gov National Institute of Standards and Technology Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2 Building 535A Upton NY, 11973 My homepage: http://xafs.org/BruceRavel EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/