Kuniko Hayakawa

Full-potential multiple scattering for x-ray spectroscopies

We present a full-potential multiple scattering (FPMS) scheme for the interpretation of several x-ray spectroscopies that is a straightforward generalization of the more conventional muffin-tin version. Like this latter, it preserves the intuitive description of the physical process under consideration and overcomes some of the limitations of the existing FPMS codes. It hinges on a fast and efficient method for solving the single-cell scattering problem that avoids the convergence drawbacks of the angular momentum expansion of the cell shape function; it relies on an alternative derivation of the multiple scattering equations that allows us to work reliably with only one truncation parameter, i.e., the number of local basis functions in the expansion of the global scattering function determined by the classical relation

Direct Deconvolution of Two-State Pump-Probe X-ray Absorption Spectra and the Structural Changes in a 100 ps Transient of Ni(II)-tetramesitylporphyrin

{l}_{\mathrm{max}}\ensuremath{\sim}kR

Full-potential multiple scattering for core electron spectroscopies

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Multiple scattering theory for non-local and multichannel potentials

Full multiple scattering (FMS) Minuit XANES (MXAN) has been combined with laser pump-probe K-edge X-ray absorption spectroscopy (XAS) to determine the structure of photoexcited Ni(II)tetramesitylporphyrin, Ni(II)TMP, in dilute toluene solution. It is shown that an excellent simulation of the XANES spectrum is obtained, excluding the lowest-energy bound-state transitions. In ground-state Ni(II)TMP, the first-shell and second-shell distances are, respectively, d(Ni-N) = (1.93 +/- 0.02) A and d(Ni-C) = (2.94 +/- 0.03) A, in agreement with a previous EXAFS result. The time-resolved XANES difference spectrum was obtained (1) from the spectra of Ni(II)TMP in its photoexcited T(1) state and its ground state, S(0). The XANES difference spectrum has been analyzed to obtain both the structure and the fraction of the T(1) state. If the T(1) fraction is kept fixed at the value (0.37 +/- 0.10) determined by optical transient spectroscopy, a 0.07 A elongation of the Ni-N and Ni-C distances [d(Ni-N) and d(Ni-C)] is found, in agreement with the EXAFS result. However, an evaluation of both the distance elongation and the T(1) fraction can also be obtained using XANES data only. According to experimental evidence, and MXAN simulations, the T(1) fraction is (0.60 +/- 0.15) with d(Ni-N) = (1.98 +/- 0.03) A (0.05 A elongation). The overall uncertainty of these results depends on the statistical correlation between the distances and T(1) fraction, and the chemical shift of the ionization energy because of subtle changes of metal charge between the T(1) and S(0) states. The T(1) excited-state structure results, independently obtained without the excited-state fraction from optical transient spectroscopy, are still in agreement with previous EXAFS investigations. Thus, full multiple scattering theory applied through the MXAN formalism can be used to provide structural information, not only on the ground-state molecules but also on very short-lived excited states through differential analysis applied to transient photoexcited species from time-resolved experiments.

Nanoclusters Synthesized by Synchrotron Radiolysis in Concert with Wet Chemistry

We present a rigorous derivation of a real space full-potential multiple-scattering theory (FP-MST), valid both for continuum and bound states, that is free from the drawbacks that up to now have impaired its development, in particular the need to use cell shape functions and rectangular matrices. In this connection we give a new scheme to generate local basis functions for the truncated potential cells that is simple, fast, efficient, valid for any shape of the cell and reduces to the minimum the number of spherical harmonics in the expansion of the scattering wavefunction. This approach provides a straightforward extension of MST in the muffin-tin (MT) approximation, with only one truncation parameter given by the classical relation l(max) = kR(b), where k is the photo-electron wavevector and R(b) the radius of the bounding sphere of the scattering cell. Some numerical applications of the theory are presented, both for continuum and bound states.

Progresses in the MXAN Fitting Procedure

Methodological advances in multiple scattering theory (MST) in both wave and Greens function versions are reported for the calculation of electronic ground and excited state properties of condensed matter systems with an emphasis on core-level photoemission and absorption spectra. Full-potential MST is reviewed and extended to non-local potentials. Multichannel MST is reformulated in terms of the multichannel density matrix whereby strong electron correlation of atomic multiplet type can be accounted for in both ground and excited states.

Scissors mode and dichroism in an anisotropic crystal

Wet chemical reduction of metal ions, a common strategy for synthesizing metal nanoparticles, strongly depends on the electric potential of the metal, and its applications to late transition metal clusters have been limited to special cases. Here, we describe copper nanoclusters grown by synchrotron radiolysis in concert with wet chemistry. The local structure of copper aggregates grown by reducing Cu(II) pentanedionate using synchrotron x-ray beam was studied in situ by x-ray absorption spectroscopy. A detailed analysis of the XANES and EXAFS spectra, compared with DFT calculations and full-potential non-muffin-tin multiple scattering calculations, identified the nanocluster as Cu13 with icosahedral symmetry. The novel “charged” nanoclusters tightly bound to electron-donating amido molecules, which formed as a result of photo-induced deprotonation of ligand amines, were stabilized by irradiation. Monodispersive deposition of nanoclusters was enabled by controlling the type and density of “monomers”, in remarkable contrast to the conventional growth of metallic nanoparticles.

Scissors Modes in crystals with cubic symmetry

Recently, a new method (MXAN) of extracting the local structural information available in the XANES spectra has been developed in the framework of the multiple scattering theory and successfully applied to the analysis of several system, both in solid and liquid state, In this paper we show the progress we have done in the MXAN procedure, in particular for what concerns the phenomenological broadening and the electronic charge fitting. We have also implemented parallelization on MXAN code by MPI library for both energy points and annealing for no‐structure parameters. This approach reduce the computer time of a factor ≈ 10 ( our cluster contains 14 nodes but the computer times scales with the number of nodes ) and at the same time increase the accuracy of the method. The new version of the program will be discussed on the basis of several examples.

A two rotor model with spin for magnetic nanoparticles

We suggest that in an anisotropic crystal there should be a mechanism of dichroism related to a scissors mode, a kind of excitation observed in several other many-body systems. Such an effect should be found in crystals, amorphous systems, and also metalloproteins. Its signature is a strong magnetic dipole transition amplitude, which is a function of the angle between the momentum of the photon and the anisotropy axis of the cell.

Full potential multiple scattering calculations of transition metals K-edges

AbstractWe recently suggested that the Scissors Mode (a collective excitation in which one system rotates with respect another one conserving its shape) can occur in crystals with axially symmetric atoms as a precession of these atoms around the anisotropy axis of their cells, giving rise to a form of dichroism. In the present paper we investigate how the Scissors Mode can be realized in crystals with cubic symmetry and evaluate its photo-absorption cross-section. This turns out to be of the same order of magnitude as that for crystals with axially symmetric atoms, but does not exhibit any correlation between the direction of the photon and the axes of the cell.