Motivation#
Feff is a collection of programs for calculating X-ray absorption and related spectroscopies. The code and research that went into the physical insight for these calculations originated with the work of John Rehr and his research group. The work here focuses on some of the earliest codes from Rehr’s group to calculate EXAFS contrubutions for selected photoelectron scattering paths for an absorber and scatterer pair. In fact, the emphasis is on fist-shell scattering, or near-neighbor paths which usually dominate the EXAFS scattering and can be used in a semi-automated way.
Feff calclulates EXAFS for each scattering path taken by the photo-electron. While setting up a calculation is not too difficult, and running the Feff program to do the calculation is not too slow, it is still some work, and it is possible to make some bad (or even “wrong”) choices, and end up with a problematic result. Using the calculation results is also not too difficult, but not exactly trivial. Still, in the most general case, a calculation needs to be done.
To do the Feff calculation, you need to have a cluster of atoms, and identify the absorbing atom and X-ray edge. The atomic cluster does not need to be too big, or generated from a crystal structure, but this is an easy way to start, and the expectation for the calculations here.
FeffDB is a collection of Feff EXAFS calculations – effectively, the
feff0001.dat (and maybe feff0002.dat) files for the first
neighbor from running Feff (all the results are currently from
Feff8L). When possible (and for all current examples), the content of
the feff.inp file used for the calculation, and the CIF file used
to generate that feff.inp file are also included in the database.
The data are stored in a single file (typically called feffdat.db) that is an SQLite3 database. This stores data in a number of Tables, with columns of fixed name and intended meaning, but many rows, one for each entry.