Running a XANES Simulation
A Basic Outline
I. Herman – Skillman : Atomic Properties calculated self-consistently(non-relativistic) from a trial potential.
A. Build the input files for each unique atom (different elements or ionicities)
1. Requires the electronic structure for the atom – see [PT]
2. Requires an initial trial potential for the atom – see [HS]
3. Requires energy eigenvalues of the subshells – see [HS] or [XPS]
4. Requires a parameter for Xa exchange potential term – see [KS]
5. Fill in control parameters, title, etc.
B. Run the program for each unique atom
1. Keep hsinfo.out for the calculated energy eigenvalues
2. Keep hswf.out and/or hspot.out for the calculated radial wavefunctions and potentialReferences
II. Muffin-Tin Potential : Crystal Scattering Phase Shifts and Atomic EXAFS Matrix Elements calculated from the crystal potential. The lattice potential can be calculated from inputted wavefunctions or can be given.
A. Build the input files for the crystal
1. xt.dat : Crystal lattice and program controls
a. Requires the lattice unit cell and basis – see [WK]
b. Requires a parameter of each unique atom for Xa multiple scattering – see [KS]
c. Requires atomic or ionic radii of each unique atom – see [PT]
d. Requires subshell energy eigenvalues from Herman-Skillman
e. Requires knowledge of the experimental parameters
f. Fill in control parameters, titles, output choices, etc.
•IPX = 0 for scattering phase shifts dl; set L = max. angular momentum state calculated
•IPX = 1 for EXAFS matrix elements <M>; set L = emitter initial angularm momentum state
2. wf.dat; Option HERMAN-S : Wavefunctions in Herman-Skillman form; used to calculate a muffin-tin potential for the lattice which can be used to calculate the scattering phase shifts or the EXAFS matrix elements.
a. Requires wavefunctions for each unique atom
3. wf.dat; Option POTENTIA : Potential for the emitter atom; used to calculate the scattering phase shifts.
a. Requires the pre-determined lattice potential for the emitter atom
B. Run the program twice.
1. Scattering Phase Shifts, dl
a. Use the version of xt.dat set up with IPX = 0.
b. Use the appropriate wf.dat Option: HERMAN-S or POTENTIA
c. Keep muf8.out for the guaranteed real phase shifts. Option HERMAN-S will contain the phase shifts for each unique atom in the lattice while Option POTENTIA will contain only the emitter atom phase shifts.
d. Keep muf9.out for the alternate calculation of the real AND imaginary phase shifts.
2. EXAFS Matrix Elements, <M>
a. Use the version of xt.dat set up with IPX = 1.
b. Use the wf.dat Option HERMAN-S.
c. Keep muf8.out for the emitter matrix elements.[HS] Herman, Frank and Skillman, Sherwood, Atomic Structure Calculations,
III. XANES (NEXAFS) : X-ray Absorption Fine Structure within about 50eV of the edge calculated by multiple scattering in a spherical cluster geometry .
Download current release xanes.uw.v06.00 August 2002 tar-gzip
Download sample inputs and outputs for xanes.uw.v06.00 August 2002 tar-gzip
Improvements beyond 1986 CPC version include ability to declare crystalline versus polycrystalline sample, ability to calculate emission from either an s-state or a p-state excitation, ability to include the imaginary part of the scattering phase shifts, inclusion of Fermi level offset and experimental detector resolution along with a Seah and Dench Universal Curve determination of the attenuation length. Also, the array declarations are improved so the program can be cleanly compiled with a -r8 or similar option forcing all reals to be double precision. Successfully compiled on a COMPAQ ALPHA TRU64 V4.0F, AMD PC LINUX, SGI IRIX 6.1.
A. Build the input files for the cluster
1. unit4.dat : Program control data
a. Requires knowledge of the cluster
b. Requires knowledge of the experimental parameters
c. Fill in control parameters, titles, output choices, etc.
2. unit5.dat : Cluster information
a. Requires the cluster corresponding to the crystal defined by xt.dat from the muffin-tin potential.
b. Requires the scattering phase shifts for each unique atom from the muffin-tin potential.
c. Requires the EXAFS matrix elements for the emitter atom from the muffin-tin potential.
d. Fill in control parameters, titles, etc.
B. Run program 1 of xanes
1. Keep xn1.tauz.out; it is the calculated reflection matrix
C. Run program 2 of xanes
1. Keep xn2.8.out for the theoretical absorption spectra
- [HS] Herman, Frank and Skillman, Sherwood, Atomic Structure Calculations, Prentice-Hall, Inc., Englewood Cliffs, New Jersey, 1963.
- [KS] Karlheinz Schwarz, Phys. Rev. B 5 Num. 7, 2466 (1972).
- [PT] Periodic Table; http://www.webelements.com
- [WK] Wyckoff, Ralph W. G., Crystal Structures, Interscience Publishers, NY, 1965.
- [XPS] Handbook of X-ray Photoelectron Spectroscopy, Perkin-Elmer.