FEFF8 calculates extended x-ray-absorption fine structure (EXAFS), x-ray-absorption near-edge structure (XANES) and local densities of state (LDOS), using an ab initio self-consistent real space multiple scattering (RSMS) approach for clusters of atoms (Z < 97), including polarization dependence. Calculations are based on an all-electron, relativistic Green's function formalism. The method combines both full multiple scattering and a high-order path expansion based on the Rehr-Albers multiple scattering formalism. Spin dependent calculations of x-ray magnetic circular dichroism (XMCD) and spin polarized x-ray absorption (SPXAS and SPEXAFS) are also possible with overlapped atomic potentials, but much less automated.
For a quick start we suggest that users try a few the examples in Section 4. For details on use of the code, examples and suggestions for calculation strategies, see Sections 2, 3, and 4. For details about the algorithms used see the discussion for the appropriate module in Section 2 and, for more detail, the published references listed in Appendix C.
FEFF is written in ANSI Fortran 77, with the non-standard extension of double precision complex (complex*16) variables. It requires at least 18 megabytes (MB) of available memory (RAM) to run. For XANES calculations, one generally needs more memory (about 60 MB of RAM for a cluster of 100 atoms, about 170 MB for a cluster of 200 atoms, and so on). For self-consistent calculations 20 MB of available free space on a diskdrive is required. See Appendix B for installation instructions.
The main developers of FEFF8 are:
Contact the authors concerning any problems with the code. See Appendix F for trouble-shooting hints and problem/bug reports.
FEFF8 is copyright protected software and users must obtain a license from the University of Washington Office of Technology Transfer for its use. See Appendix A for complete copyright notice and other details. Documentation and information on how to obtain the code can be found at the FEFF Project WWW URL:
or by e-mail to the FEFF Project Coordinator at firstname.lastname@example.org.
Please cite FEFF and an appropriate FEFF reference if the code or its results are used in published work. See Appendix C for a list of appropriate citations. The main published reference for FEFF8 is: Real Space Multiple Scattering Calculation and Interpretation of X-ray Absorption Near Edge Structure, A.L. Ankudinov, B. Ravel, J.J. Rehr, and S.D. Conradson Phys. Rev. B58, 7565 (1998).
Several new features have been added to FEFF8 compared to FEFF7 and earlier versions of FEFF. Alexei Ankudinov developed the automated self-consistent potential algorithm, and added calculations of LDOS, the Fermi level, and charge transfer. Bruce Ravel developed the full multiple scattering (FMS) algorithm, which is necessary for DOS and for many XANES calculations. Anna Poiarkova contributed two new codes for calculating multiple-scattering Debye-Waller factors. Matthew Newville added an improved output structure to facilitate the interface to XAFS analysis codes. The high-order multiple-scattering routines, pathfinder, and input/output routines were developed by Steven Zabinsky for FEFF5 and 6, and are still in use. The Hedin-Lundqvist self-energy and phase shift routines were developed for early versions of FEFF in collaboration with Jose Mustre de Leon, Dan Lu and R.C. Albers and are still part of FEFF8. The authors thank many users of experimental versions of the FEFF8 code for feedback and suggestions. The authors also thank R.C.\ Albers, K. Baberschke, C. Brouder, G. Brown, S.D. Conradson, G.\ Hug, M. Jaouen, and E. Stern for useful comments.