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5. A Worked Example

Here is an example of atoms in action. The material is Lead Titanate, PbTiO3. The crystallographic literature places this material in the tetragonal space group P 4 M M. The data was taken in fluorescence at the titanium K-edge. Since the edge energy is around 5 KeV and the sample was very thick, the I0 and self-absorption corrections are expected to be significant. That titanium is the central atom is indicated by the keyword core. atoms assumes the K-edge of the titanium was probed because the atomic number of titanium is less than 57 and the edge was not otherwise chosen with the edge keyword. The I0 chamber was filled with 92% helium and 8% nitrogen by pressure. This is indicated by the nitrogen keyword. The indexing feature is engaged with the index keyword. The size of the cluster to be printed in feff.inp is chosen with the rmax keyword.

        title PbTiO3 10K,a=3.885,c=4.139
        space  P 4 m m
        a=3.885         c=4.139         nitrogen = 0.08   
        index=true      rmax=4.2        core=ti
        atom
        ! At.type  x        y       z      tag
           Pb     0.0      0.0     0.0     
           Ti     0.5      0.5     0.5377  
           O      0.5      0.5     0.1118  axial
           O      0.0      0.5     0.6174  planar
        -------------------------------------------------

atoms produces the output reproduced below. The absorption and correction calculations are at the top of the file. All the CONTROL cards are set to 1 and the PRINT cards are set to 0. This will run all four modules of feff and produce the default output files. Several other useful feff cards are printed but commented out by an asterisk (*). The unique potential list is constructed in a simple fashion -- the core atom is potential 0 and each different atomic species has a single potential. The atom list is printed in the format required by feff. The atom list has two comment columns. The indexed atomic symbol and radial distance are written by atoms for your use when reading feff.inp and are ignored by feff.

feff will run to completion using the input file generated by atoms. It is still likely that the user will want to edit feff.inp. Several assumptions are made by atoms that might not hold true. The assignment of unique potentials is made by a simple algorithm and may not adequately reflect the physics of the problem. The CONTROL cards are such that all four modules of feff will be run. The feff user might want to run the modules separately. Values for other cards have been assumed and might not be desired. Other cards have been left out entirely. Always check your feff.inp file to be sure it is just what you want.

 * This feff.inp file generated by ATOMS, version 2.44a
 * ATOMS written by Bruce Ravel and copyright of The Univ. of Washington, 1994

 * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- *
 *       total mu =     5269.6 cm^-1, delta mu =      772.6 cm^-1
 *       specific gravity =  8.057, cluster contains  123 atoms.
 * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- *
 *       mcmaster corrections:   .00093 ang^2 and   .165E-05 ang^4
 *       self-abs. corrections: amplitude factor =  1.087
 *                               .00004 ang^2 and   .461E-07 ang^4
 *       i0 corrections:         .00118 ang^2 and   .122E-05 ang^4
 * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- *
 *       sum of corrections:     .00216 ang^2 and   .292E-05 ang^4
 * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- *
  
 TITLE   PbTiO3 10K a=3.885 c=4.139                                            
  
 HOLE 1   1.0     Ti K edge  (  4.965 keV), s0^2=1.0
  
 *         mphase,mpath,mfeff,mchi
 CONTROL   1      1     1     1
 PRINT     0      0     0     0
  
 RMAX     4.139
  
 *CRITERIA     curved   plane
 *DEBYE        temp     debye-temp
 *NLEG         8
 *XANES
  
 POTENTIALS
 *   ipot   z  label
       0   22   Ti
       1    8   O 
       2   82   Pb
       3   22   Ti
  
 ATOMS
    .00000      .00000      .00000    0   Ti_00             .00000
    .00000      .00000    -1.76280    1   axial_01         1.76280
   1.94250      .00000      .32988    1   planar_01        1.97031
    .00000     1.94250      .32988    1   planar_01        1.97031
  -1.94250      .00000      .32988    1   planar_01        1.97031
    .00000    -1.94250      .32988    1   planar_01        1.97031
    .00000      .00000     2.37620    1   axial_02         2.37620
   1.94250    -1.94250     1.91346    2   Pb_01            3.34783
  -1.94250    -1.94250     1.91346    2   Pb_01            3.34783
  -1.94250     1.94250     1.91346    2   Pb_01            3.34783
   1.94250     1.94250     1.91346    2   Pb_01            3.34783
   1.94250     1.94250    -2.22554    2   Pb_02            3.53548
  -1.94250    -1.94250    -2.22554    2   Pb_02            3.53548
  -1.94250     1.94250    -2.22554    2   Pb_02            3.53548
   1.94250    -1.94250    -2.22554    2   Pb_02            3.53548
    .00000     3.88500      .00000    3   Ti_01            3.88500
  -3.88500      .00000      .00000    3   Ti_01            3.88500
    .00000    -3.88500      .00000    3   Ti_01            3.88500
   3.88500      .00000      .00000    3   Ti_01            3.88500
    .00000      .00000     4.13900    3   Ti_02            4.13900
    .00000      .00000    -4.13900    3   Ti_02            4.13900
 END


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