International
Tables for
Crystallography
Volume I
X-ray absorption spectroscopy and related techniques
Edited by C. T. Chantler, F. Boscherini and B. Bunker

International Tables for Crystallography (2022). Vol. I. Early view chapter
https://doi.org/10.1107/S1574870720016730

Validation procedures for XAFS

James R. Hestera*

aAustralian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia
Correspondence e-mail: james.hester@ansto.gov.au

Suggested validation checks for XAFS data sets are tabulated together with the datafile contents necessary to carry out these checks.

Keywords: validation procedures.

1. Introduction

Well defined machine-readable metadata allow the automatic validation of internal data-set consistency and are a useful tool for both developing and promoting community standards for data presentation. For example, CheckCIF (Strickland et al., 2006[link]) includes an extensive set of data-validation routines applied to datafiles written according to the CIF standards, and is widely used by structure-publishing journals to assess the quality of the experiment upon which a crystal structure is based; with the advent of agreed XAFS metadata definitions and file formats, similar levels of validation would be possible for XAFS data.

2. Required metadata

A shared and well defined collection of data names allows journals, peak XAFS bodies and XAFS databases to specify data names that should be included in a datafile in order to meet a particular standard. Initial validation then checks for the presence of these data names. A further level of validation examines data-name values to ensure that they are both within acceptable ranges and self-consistent. Table 1[link] lists some possible XAFS datafile consistency checks, together with generic data names that must be included in the file in order to carry out the checks. Note that many data names for describing crystal structures have already been defined within the Crystallographic Information Framework and need not be redefined for XAFS work.

Table 1
Example validation checks for an XAFS datafile

Data-processing stageValidation checkRequired data names (in general may take multiple values)
Raw data Do the reported data correspond to the specified experimental setup? Detector type, detector position, number of fluorescence detector channels, measured detector signal
Are ionization detector counts provided for all detectors?
If fluorescence detector counts are included, has the detector been described?
Are any data channels missing?
Data reduction Have the absorption values been correctly derived from the observed counts (including error propagation)? Energy, wavelength, monochromation type, monochromator parameters, absorption, sample thickness, sample phase composition, measured sample density, absorption edge name
Is the stated sample composition and thickness approximately consistent with the observed absorption?
Does the absorption edge occur in the correct region?
Have multiple channels been correctly merged?
Have monitor counts been correctly applied?
Have out-of-range detector readings been appropriately handled?
Has wavelength been correctly converted to energy?
Data fitting Does subtraction of the stated background functions reproduce the provided XAFS curves? Calculated and experimental XAFS, k value, coefficients in equation for pre-edge background, spline coefficients, atomic positions, occupancies and displacement parameters, k-weighting scheme, Fourier filter settings, source of theoretical XAFS calculations
Does the stated atomic model reproduce the fit?
Are the fitting statistics correct?
Is the atomic model chemically reasonable?

References

First citationStrickland, P., Hoyland, M. A. & McMahon, B. (2006). International Tables for Crystallography, Vol. G, edited by S. R. Hall & B. McMahon, pp. 561–562. Dordrecht: Springer.Google Scholar








































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