ELNES

From FEFF

Standard

ELNES [xkmax xkstep vixan]
E [aver [cross [relat]]]
kx ky kz
beta alfa
nr na
dx dy
  • xkmax

The maximum k-value for the calculation. xkmax, xkstep and vixan are exactly the same parameters as those used for the XANES card.

  • xkstep

The step size of the upper part of the k-mesh

  • vixan

The step size of the lower part of the k-mesh

  • E

energy of the electron beam in keV (typical values are 100-400 keV);

  • aver

1: calculate orientation averaged spectrum (e.g., a polycrystalline sample, working at the magic angle) ; 0 : use specific sample to beam orientation (default);

  • cross

1: use cross terms for the cross section (e.g., xy or yx ; default); 0: use only direct terms (eg., atom coordinates entered in symmetric coordinate frame ; assumed as default if aver is set to 1);

  • relat

1 (default): to use relativistic formula for the cross-section (default, always recommended); 0 to use nonrelativistic formula (for checking against old results ; does not save any time!);

  • kx,ky,kz

wave vector of the incoming electron in the crystal frame (i.e., the Cartesian coordinate system in which the atom positions of the ATOMS card are given); in arbitrary units (only the direction, not the size of k is used). Note: This line should be present for orientation sensitive calculations, and absent for averaged calculations.

  • beta

the collection semiangle of the EELS detector in mrad (typical values are of the order of 1 mrad);

  • alpha

The convergence semiangle of the incoming beam in mrad (typical values are of the order of 1 mrad);

  • nr, na

The cross section is integrated over the values of impulse transfer q allowed by alpha and beta. The integration grid consists of nr concentric circles sampling a disc of radius alpha + beta. Circle i contains na * (2i - 1) points, making for nr * nr * na points total. These are nonphysical parameters and should be converged. Typical would be, e.g., 50, 1; the integration is quite fast. Only for small values of nr is it necessary to increase na above 1).

  • dx, dy

The position of the detector in the scattering plane, specified by angles in mrad along the x and y axes (the same as used in the ATOMS card) (typical values are 0.0, 0.0)

The line giving beam orientation must only be present when an oriented spectrum is calculated. The following example simulates an experiment with a 300 keV beam hitting the sample along the y-axis. The detector is set in the forward direction and has a 2.4 mrad (semi-)opening; the width of the incoming beam is 0 mrad. To do the integration over the detector aperture, 5*5*3 = 75 points are used. The calculation is relativistic and takes sample to beam orientation into account. Default settings are used for the energy/k-mesh.

ELNES # calculate elnes.
300 # beam energy in keV
0 1 0 # beam direction in the crystal frame
2.4 0.0 # collection semiangle, convergence semiangle (in mrad)
5 3 # q-integration mesh : radial size, angular size
0.0 0.0 # position of the detector (x,y angle in mrad)
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