Application of RMC method for X-ray absorption spectra interpretation

Inga Jonāne (ISSP UL EXAFS laboratory)

Analysis of X-ray absorption fine structure is widely used for the analysis of local electronic and atomic structure of a material. Extended X-ray Absorption Fine Structure (EXAFS) contains information about the chemical composition of the sample, interatomic distances, amplitudes of atomic oscillations, strength of chemical bonds and other related quantities.

EXAFS experiments are carried out at synchrotron radiation facilities. During these experiments, attenuation of X-rays with the energy close to the absorption edge of a specific chemical element is measured. This ensures chemical selectivity of the method: one can investigate the local structure of the material around atoms of specific type.

For the advanced interpretation of EXAFS data one can use different types of simulation-based methods. One of such methods is reverse Monte-Carlo (RMC) approach. This method is based on iterative random changes of atomic coordinates within a 3D model of the material, with the aim to obtain the best possible agreement between the experimental and calculated EXAFS spectra. To make this method computationally more effective, recently we have proposed to complement it with evolutionary algorithm (EA) approach [1].

In this presentation, we apply RMC/EA-EXAFS method to investigate the local structure around scandium atoms in crystalline scandium fluoride (ScF3), a perovskite-type material, which recently has attracted attention due to large negative thermal expansion of its lattice in a broad temperature range [2].


[1]J.Timoshenko, A.Kuzmin, J.Purans,J. Phys.: Condens. Matter 26, 055401 (2014)

[2] Greve B. K., Martin K. L, et a.l, Journal of the American Chemical Society, 132(44) (2010)