Main Control Cards

 

These cards in this section are not associated with any particular module, but are used throughout the FEFF calculation. The ATOMS card is used to specify the absorbing atom and its environment. (If atomic coordinates are not known, then the OVERLAP card can be used to construct approximate potentials). Without this structural information no calculations can be done. The CONTROL card is used to selectively run parts of FEFF. The PRINT card controls which output files are written by the modules.

 ATOMS        (Standard)

Cartesian coordinates (in Ångstroms) and unique potential indices of each atom in the cluster are entered following the ATOMS card, one per line. See also the discussion of the POTENTIALS card. An auxiliary code, ATOMS written by Bruce Ravel, is supplied with FEFF to generate the ATOMS list from crystallographic data. See the document file for ATOMS for more information.

  ATOMS
  * x      y      z     ipot     SF6 molecule
    0.0    0.0    0.0     0      S K-shell hole

    3.61   0.00   0.00    1      F 1st shell atoms
    0.00   3.61   0.00    1
    0.00   0.00   3.61    1
   -3.61   0.00   0.00    1
    0.00  -3.61   0.00    1
    0.00   0.00  -3.61    1

 CONTROL    ipot ixsph ifms ipaths igenfmt iff2chi    (Standard)

The CONTROL card lets you run one or more of the modules separately. There is a switch for each module: 0 means not to run that module, 1 meaning to run it. You can do the whole run in sequence, one module at a time, but you must run all modules sequentially. Do not skip modules: CONTROL 1 1 1 0 0 1 is incorrect. The default is CONTROL 1 1 1 1 1 1, i.e. run all 6 modules.

  * example 1
  * calculate self consistent potentials, phase shifts and fms only
  CONTROL  1 1 1 0 0 0   ipot  ixsph  ifms   ipaths  igenfmt  iff2chi

  * example 2
  * run paths, genfmt and ff2chi; do not run pot, xsph, fms
  * this run assumes previous modules have already been run and
  * adds MS paths between rfms  and rpath to the MS expansion
  CONTROL  0 0 0 1 1 1    ipot  ixsph  ifms   ipaths  igenfmt  iff2chi

 PRINT    ppot pxsph pfms ppaths pgenfmt pff2chi    (Standard)

The PRINT card determines which output files are printed by each module. The default is print level 0 for each module. See Section 3 for details about the contents of these files.

  * add crit.dat and feffNNNN.dat files to minimum output
  PRINT  0  0  0  1  0  3

The print levels for each module are summarized in Table 2.1 on page .

  
Table 2.1: Print levels controlling output files from the modules.

 TITLE    title_line    (Standard)

User supplied title lines. You may have up to 10 of these. Titles may have up to 75 characters. Leading blanks in the titles will be removed.

TITLE  Andradite  (Novak and Gibbs, Am.Mineral 56,791 1971)
TITLE  K-shell 300K

 END        (Useful)

The END card marks the end of portion of the 'feff.inp' file read by FEFF. All data following the END card is ignored. Without an END card, the entire input file is read.

END    ignore any lines in feff.inp that follow this card

 RMULTIPLIER    rmult    (Useful)

With RMULTIPLIER all atomic coordinates are multiplied by the supplied value. This is useful to adjust lattice spacing, for example, when fractional unit cell coordinates are used. By default, rmult=1.

*increase distances by 1%
RMULTIPLIER 1.01

 CFAVERAGE    iphabs nabs rclabs    (Advanced)

A ``configuration'' average over absorbers is done if the CFAVERAGE card is given. CFAVERAGE currently assumes phase transferability, which is usually good for EXAFS calculations, but may not be accurate for XANES. Note that the CFAVERAGE card is currently incompatible with the NOGEOM card and with the DEBYE card for options other than correlated Debye model ().

iphabs

potential index for the type of absorber to over which to make the configuration average (potential 0 is also allowed)

nabs

the configuration average is made over the first nabs absorbers in the 'feff.inp' file of type iphabs. You don't have to have potential of index 0 in your input file when using the CFAVERAGE card, but you must have the same type of potential for iph=0 and iph=iphabs. The configurational average is done over ALL atoms of type iphabs, if nabs is less or equal zero.

rclabs

radius to make small atom list from a bigger one allowed in 'feff.inp'. Currently the parameter controlling the maximum size of the list, natxx, is 100,000 but can be increased. The pathfinder will choke on too big an atoms list. You must choose rclabs to have less than 1,000 atoms in small atom list. If your cluster is less 1000 atoms simply use rclabs=0 or negative always to include all atoms.

Default values are iphabs=0, nabs=1, rclabs=0 (where means to consider an infinite cluster size).

*average over all atoms with iph=2 in feff.inp with less than 1000 atoms
CFAVERAGE 2  0  0

 OVERLAP    iph    (Advanced)

The OVERLAP card can be used to construct approximate overlapped atom potentials when atomic coordinates are not known or specified. If the atomic positions are listed following the ATOMS cards, the OVERLAP cards are not needed. FEFF8 will stop if both ATOMS and OVERLAP cards are used. The OVERLAP card contains the potential index of the atom being overlapped and is followed by a list specifying the potential index, number of atoms of a given type to be overlapped and their distance to the atom being overlapped. The examples below demonstrate the use of an OVERLAP list. This option can be useful for initial single scattering XAFS calculations in complex materials where very little is known about the structure.

You should verify that the coordination chemistry built in using the OVERLAP cards is realistic. It is particularly important to specify all the nearest neighbors of a typical atom in the shell to be overlapped. The most important factor in determining the scattering amplitudes is the atomic number of the scatterer, but the coordination chemistry should be approximately correct to ensure good scattering potentials. Thus it is important to specify as accurately as possible the coordination environment of the scatterer. Note: If you use the OVERLAP card then you cannot use the FMS or SCF cards. Also the pathfinder won't be called and you must explicitly specify single scattering paths using SS card, which is described in Section 2.6.

* Example 1. Simple usage
* Determine approximate overlap for central and 1st nn in Cu
OVERLAP 0         determine overlap for central atom of Cu
  *iphovr   novr   rovr       * ipot, number in shell, distance
   1        12     2.55266
OVERLAP 1         determine approximate overlap for 1st shell atoms
  *iphovr   novr   rovr       * ipot, number in shell, distance
   0        12     2.55266

* Example 2. More precise usage
* Determine approximate overlap for 3rd shell atoms of Cu
OVERLAP 3
  0  1 2.55266    ipot, number in shell, distance
  1  4 2.55266
  2  7 2.55266
  2  6 3.61000
  2 24 4.42133