K-space FEFF

From FEFF

Although feff is traditionally a real-space code, the current version feff9 is capable of calculating infinite periodic systems (crystals) in reciprocal space. The reciprocal space engine is based on impurity KKR. This new functionality is implemented through a handful of new input CARDs. The main difference from the real-space code is that the system is specified in terms of a unit cell with lattice vectors and a basis of atoms in the unit cell, instead of a real space cluster. We will describe how to do this below.

The RECIPROCAL card is a switch that tells feff to work in k-space. First of all, the crystal structure must be specified. This can be done in two ways. The recommended way (new as of feff-9.5.1) is to use the CIF card to specify the name of a ‘*.cif’ file containing the crystal structure. The second way, which was teh default in prior feff versions but is less user-friendly and more error-prone, is to use the following CARDs in ‘feff.inp’ : the LATTICE card gives the basis vectors spanning the unit cell ; and the ATOMS card lists all atoms in the unit cell. In both cases, the TARGET card places the absorber on one of the sites (either the list of sites in the ATOMS card, or the list of sites in the ‘.cif’ file) ; and the KMESH card sets the size of the mesh used to sample Brillouin Zone integrals. There are also a few optional cards, notably COORDINATES (sets the units for the ATOMS card if one uses the LATTICE/ATOMS approach), SGROUP (only for the LATTICE/ATOMS approach) and BANDSTRUCTURE (currently inactive), and STRFAC (a developers card that is not usually needed).

In the JFEFF GUI only the CIF method is supported. Select ”Import CIF file” from the ”Atoms” pulldown menu. A ”Select CIF file” appears, and in the ”General” tab in the bottom pane the RECIPROCAL, TARGET, KMESH, and STRFAC cards become active. If you click the ”Jmol” button, you will see the unit cell (only the generating atom positions are shown).

If a core hole is needed, we recommend using COREHOLE RPA. Note that NRIXS cannot currently be run in k-space.

  1. Notes on using a .cif file
  2. Using the file reciprocal.inp
  3. Converging the k-mesh
  4. EXAFS and EXELFS
  5. Using crystal symmetry
  6. Speed
  7. Example Input Files
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