Calogero R. Natoli

The MXAN procedure: a new method for analysing the XANES spectra of metallo­proteins to obtain structural quantitative information

The first quantitative analyses are reported of the Fe K-edge polarized X-ray absorption near-edge structure (XANES) of a single crystal of the iron protein carbonmonoxy-myoglobin (MbCO) and of its cryogenic photoproduct Mb*CO. The CO-Fe-heme local structure has been determined using a novel fitting procedure, named MXAN, which is able to fit the XANES part (from the edge to about 200 eV) of experimental X-ray absorption data. This method is based on the comparison between the experimental spectrum and several theoretical spectra that are generated by changing the relevant geometrical parameters of the site around the absorbing atom. The theoretical spectra are derived in the framework of the full multiple-scattering approach. The MXAN procedure is able to recover information about the symmetry and atomic distances, and the solution is found to be independent of the starting conditions. The extracted local structure of Mb*CO includes an Fe-CO distance of 3.08 (7) A, with a tilting angle between the heme normal and the Fe-C vector of 37 (7) degrees and a bending angle between the Fe-C vector and the C-O bond of 31 (5) degrees

X-ray absorption spectroscopy: state-of-the-art analysis.

State-of-the-art techniques for analysing X-ray absorption spectra are reviewed, with an eye to biological applications. Recent attempts to perform full spectral fitting of the XANES energy region and beyond for the purpose of structural analysis have met with encouraging success. The present paper analyses the theoretical motivations behind this success and indicates routes for future improvements. The theoretical background is not entirely new, although the point of view is, and some sections and appendices present material that the Authors believe has never been published before. The aim of this paper is to provide a theoretical analysis that is as self-contained as possible.

X-ray natural circular dichroism in a uniaxial gyrotropic single crystal of LiIO3

We produce the first experimental evidence of x-ray natural circular dichroism (XNCD) in a uniaxial gyrotropic crystal of α-LiIO3 that is known to crystallize with space group P63 and to exhibit a very strong nonlinear susceptibility. For the sake of simplicity, the optical axis was set colinear to the direction of the exciting x-ray beam in order to get rid of undesirable birefringence and linear dichroism effects. The nicely structured XNCD spectra recorded at the LI, LII, and LIII edges of iodine are assigned to the electric dipole–electric quadrupole (E1.E2) interference terms which do not vanish in gyrotropic crystals but contribute to a second order polarizability. Our interpretation is consistent with a band structure calculation and is fully supported by ab initio multiple scattering simulations. The signatures recorded at the LII and LIII edges are similar and have the same sign. This is in contrast to x-ray magnetic circular dichroism (XMCD) spectra which usually exhibit opposite signs at the LI...

X-ray absorption spectra at the Ca L 2 , 3 edge calculated within multichannel multiple scattering theory

We report a theoretical method for x-ray absorption spectroscopy (XAS) in condensed matter which is based on the multichannel multiple scattering theory of Natoli et al. and the eigen-channel

Full-potential multiple scattering for x-ray spectroscopies

R

MSPHD: A full multiple scattering code for low energy photoelectron diffraction

-matrix method. While the highly flexible real-space multiple scattering (RSMS) method guarantees a precise description of the single-electron part of the problem, multiplet-like electron correlation effects between the photoelectron and localized electrons can be taken account for in a configuration interaction scheme. For the case where correlation effects are limited to the absorber atom, a technique for the solution of the equations is devised, which requires only little more computation time than the normal RSMS method for XAS. The method is described and an application to XAS at the Ca

Full-potential multiple scattering for core electron spectroscopies

{L}_{2,3}

Multiple scattering theory for non-local and multichannel potentials

edge in bulk Ca, CaO, and

MsSpec-1.0: A multiple scattering package for electron spectroscopies in material science

\mathrm{Ca}{\mathrm{F}}_{2}

Angle dependence of the spin-orbit branching ratio

is presented.