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Manuscript Title: Calculation of X-ray absorption near edge structure, XANES.
Authors: P.J. Durham, J.B. Pendry, C.H. Hodges
Program title: DLXANES
Catalogue identifier: AARR_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 25(1982)193
Programming language: Fortran.
Computer: NAS 7000.
Operating system: HASP.
RAM: 304K words
Word size: 32
Keywords: Surfaces, Solid state physics, X-ray absorption, Near edge, K-shell, Core level, Excited electron, Multiple scattering, Solids, Ordered, Disordered, Local structure.
Classification: 7.2.

Other versions:
Cat Id Title Reference
AARR_v1_0 0001 ICXANES CPC 40(1986)421

Revision history:
Type Tit le Reference
adaptation 0001 ICXANES See below

Nature of problem:
To calculate the transition rate for X-ray absorption close to threshold for condensed systems in which the local atomic arrangement may be complex (e.g. crystals with many atoms per unit cell, disordered systems, surfaces, etc.). We are concerned with the so-called X-ray absorption near-edge structure (XANES), within approximately 50 eV of the edge.

Solution method:
The transition rate is calculated within the dipole approximation. An atomic contribution is identified, together with modifications arising from multiple scattering of the excited electron by the surrounding atoms. This multiple scattering is calculated by means of a real space cluster approach, which is considerably more flexible than band structure methods. Structural symmetry (rotation/reflection) is exploited if it exists, but is not required.

Restrictions:
The program is currently restricted to spectra involving core levels of s-symmetry, i.e. K, L1 edges, etc. (More generally, the restriction is to spectra in which there is no interference between the l+1 and l-1 channels coupled by the dipole selection rule to a core level of angular momentum l.)

ADAPTATION SUMMARY
Manuscript Title: An update of DLXANES, the calculation of X-ray absorption near-edge structure.
Authors: D.D. Vvedensky, D.K. Saldin, J.B. Pendry
Program title: 0001 ICXANES
Catalogue identifier: AARR_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 40(1986)421
Programming language: Fortran.
Computer: CRAY-1S.
Operating system: COS.
RAM: 170K words
Word size: 64
Classification: 7.2.

Other versions:
Cat Id Title Reference
AARR_v1_0 DLXANES CPC 25(1982)193

Nature of problem:
To calculate the X-ray absorption near-edge structure (XANES), within approximately 50eV of threshold, of an atom in a complex environment (e.g.surfaces, large molecules, disordered systems) and to investigate the effects of multiple scattering upon the absorption spectrum.

Solution method:
As for DLXANES, but with additional facilities to include various approximations to multiple scattering, calculate XANES for low-symmetry sites by translating from neighbouring higher-symmetry configurations, and calculate XANES for any polarisation of the incident x-ray source.

Restrictions:
As for DLXANES, the program as written is restricted to spectra for levels of s-symmetry, i.e., K,L1,... edges. In general the restriction is to spectra for which there is no interference between the l+1 and l-1 channels coupled by the dipole selection rule to a core level of angular momentum l.

Unusual features:
Optional approximations to multiple scattering involve replacing matrix inverses by geometric series and truncated Gauss-Seidel iteration (first order renormalised forward scattering perturbation theory). Convergence criteria are discussed explicity.

Running time:
Depends strongly upon the symmetry of the cluster, any approximations to multiple scattering, the required polarisations, as well as the maximum values for single and multicentre angular momentum expansions. The test run took 10.6 CPU sec on a CRAY-1S.