# FEFF Synopsis

### From FEFF

## Synopsis

**FEFF9** calculates spectroscopic properties, including extended x-ray-absorption fine structure (EXAFS), x-ray-absorption near-edge structure (XANES), x-ray natural circular dichroism (XNCD), spin-dependent calculations of x-ray magnetic dichroism (XMCD) and spin polarized x-ray absorption (SPXAS and SPEXAFS), nonresonant x-ray emission (XES), and Non-Resonant Inelastic X-ray Spectroscopy (NRIXS). In addition the code calculates electronic structure including local densities of states (LDOS), and the x-ray elastic scattering amplitude ƒ = 0 + ƒ′ + iƒ′′ including Thomson and anomalous parts, and relativistic electron energy loss spectroscopy (EELS).

**FEFF** uses an *ab initio* self-consistent real space multiple scattering (RSMS) approach, including polarization dependence, core-hole effects, and local field corrections, based on self- consistent, spherical muffin-tin scattering potentials. Calculations are based on an all-electron, real space relativistic Green’s function formalism with no symmetry requirements. The code builds in inelastic losses in terms of a GW self-energy, and includes vibrational effects in terms of correlated Debye-Waller factors. For periodic structures reciprocal space calculations based on periodic boundary conditions are also implemented in this release. **FEFF** can use both full multiple scattering based on LU or Lanczos algorithms and a high-order path expansion based on the Rehr–Albers multiple scattering formalism.

The name **FEFF** is derived from ƒ_{eff}, the effective curved wave scattering amplitude in the modern EXAFS equation. This was the first application of the feff code, and is the basis for the multiple-scattering path-expansion in the code.

For a quick start or self-guided tutorial we suggest that new users study the tutorial chapter
2 and try a few of the examples in Section 5. For details on use of the code, examples and suggestions for calculation strategies, see Sections 3, 4, and 5. For details about the algorithms used, see the discussion for the appropriate module in Section 3. For additional details, see the published references listed in Appendix C and the **FEFF** website, http://www.feffgroup.com/.

**FEFF** is written in ANSI Fortran 90. It requires at least 250 megabytes (MB) of available memory (RAM) to run. For XANES calculations, one generally needs more memory (about 500 MB of RAM for a cluster of 100 atoms, about 750 MB for a cluster of 200 atoms, and so on). More memory may be needed on MS Windows systems. See Appendix B for installation instructions.

Please contact the authors concerning any problems with the code. See Appendix G for trouble-shooting hints and problem/bug reports or the FAQ on the feff WWW pages (http://leonardo.phys.washington.edu/feff/).