FitIt

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FitIt is graphical software to fit X-ray absorption near edge structure (XANES). It can be used to determine the values of local atomic structure parameters on the basis of minimization between theoretical and experimental spectra. It is the program for the fitting and therefore it always uses external programs, for example FEFF8 or FDMNES, for fixed geometry calculations of XANES. In order to minimize the number of such calculations, which can be very time-consuming, multidimensional interpolation algorithm is implemented into the FitIt. Such approach has allowed also to develop visual control of the fitting procedure and it is possible to vary structural parameters by sliders and immediately see the theoretical spectrum corresponding to these structural parameters. [1] [2] [3] The program is free of charge for non-commercial research and educational purposes.

PyFitIt python implementation of FitIt software was extended with additional features: Machine learning, automatic component analysis, direct geometry prediction and others. It uses ipywidgets to construct the portable GUI, supports different types of interpolation point generation (grid, random, IHS).

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The FDMNES program calculates the spectra of different spectroscopies related to the real or virtual absorption of x-ray in material. It gives the absorption cross sections of photons around the ionization edge, that is in the energy range of XANES. The calculation is performed with all conditions of rectilinear or circular polarization. In the same way, it calculates the structure factors and intensities of anomalous or resonant diffraction spectra.

FEFF is a software program used in x-ray absorption spectroscopy. It contains self-consistent real space multiple-scattering code for simultaneous calculations of x-ray-absorption spectra and electronic structure. Output includes extended x-ray-absorption fine structure (EXAFS), full multiple scattering calculations of various x-ray absorption spectra (XAS) and projected local densities of states (LDOS). The spectra include x-ray absorption near edge structure (XANES), x-ray natural circular dichroism (XNCD), and non-resonant x-ray emission spectra. Calculations of the x-ray scattering amplitude and spin dependent calculations of x-ray magnetic circular dichroism (XMCD) and spin polarized x-ray absorption spectra are also possible, but less automated.

PARATEC is a package that performs ab initio quantum mechanical total energy calculations using pseudopotentials and a plane wave basis set. PARATEC is designed primarily for a massively parallel computing platform, and can run on serial machines. Calculations of XANES within such a full-potential approach has been implemented within PARATEC.

References

  1. G. Smolentsev and A. Soldatov, Quantitative local structure refinement from XANES: multi-dimensional interpolation approach J. Synchrotron Rad. 13, 19 (2006)
  2. G. Smolentsev and A.V. Soldatov, FitIt: New software to extract structural information on the basis of XANES fitting, Comp. Mater. Sci. 39, 569 (2007)
  3. C. Battocchio, F. D’Acapito, G. Smolentsev, A.V. Soldatov, I. Fratoddi, G. Contini, I. Davoli, G. Polzonetti and S. Mobilio, XAS study of a Pt-containing rod-like organometallic polymer, Chem. Phys. 325, 422 (2006)