[Ifeffit] anisotropic Debye temperatures in reciprocal-space calculations

[Van Der Veen, Renske M.]

Dear FEFF users!

I am looking into the use of the DEBYE card in order to calculate the EELS spectrum of graphite at ~800 K. Obviously, graphite is highly anisotropic, such that it would be unphysical to use a single Debye temperature. However, the effective in-plane (a,b axes) and out-of-plane (c axis) Debye temperatures are known for graphite (2500 and 950 K, respectively). I was therefore wondering whether it is possible in FEFF9 to specify two Debye temperatures for the two different crystallographic directions.

I am calculating the (oriented) EELS spectrum of graphite in reciprocal space using the RECIPROCAL, LATTICE and ATOMS cards; see feff.inp file below. I am using FEFF version 9.05.

In case the use of Debye temperatures is not possible in this way, could anybody recommend another way to take into account the Debye-Waller factors for an anisotropic material such as graphite?

Thanks!
Best regards,
Renske van der Veen

--

Dr. Renske M. van der Veen
California Institute of Technology
Arthur Amos Noyes Laboratory of Chemical Physics
1200 E California Blvd
MC 127-72, Pasadena, CA 91125, USA

Office: (+1) (626) 395 6530
Mobile: (+1) (626) 808 2635

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 TITLE graphite

*  C K edge energy = 284.20 eV
 EDGE      K  0.0
 CONTROL   1      1     1     1     1      1
 PRINT     1 1 1 1 1 1

COREHOLE RPA

LDOS -20 10 0.05   * this calculates the density of states

EGRID
e_grid -3 17 0.3
e_grid last 30 0.4
e_grid last 58 1

ELNES
200   # beam energy in keV
0 0 1  # beam direction in the crystal frame
10 5 # collection semiangle, convergence semiangle (in mrad)
200 1  # q-integration mesh : radial size, angular size
0.0 0.0 # position of the detector (x,y angle in mrad)

 FMS       7.0 2
 EXCHANGE  0      1   0.7
 SCF       5
 RPATH     0.2

 POTENTIALS
 *    ipot   Z  element            l_scmt  l_fms   stoichiometry
        0    6   C                  3       2       0.01
        1    6   C                  3       2       2
        2    6   C                  3       2       2

 RECIPROCAL
 KMESH 5000
 MARKER 1

 LATTICE P 2.4612
     0.86603     -0.50000      0.00000
     0.00000      1.00000      0.00000
     0.00000      0.00000      2.72546

 ATOMS                          * this list contains 251 atoms
* *   x          y          z      ipot  tag           distance
      0.00000      0.00000      0.68160  1  C1
      0.00000      0.00000      2.04479  1  C1
      0.57735      0.00000      0.68160  2  C2
      0.28868      0.50000      2.04479  2  C2
 END






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