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PhD thesis (H/F) Simulating resonant inelastic x-ray scattering across the whole periodic table

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Français - Anglais

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General information

Reference : UMR8523-ANDSEV-001
Date of publication : Saturday, February 01, 2020
Scientific Responsible name : André SEVERO PEREIRA GOMES
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 May 2020
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly

Description of the thesis topic

Spectroscopic approaches that probe core (innermost) electrons excitations with X-rays offer distinct advantage over valence ones (VU-visible and near-IR) in terms of selectivity and sensitivity. Moreover, since excitations of core electrons require extremely large energies, any small perturbation, such as hydrogen bonds or long-range coulomb interactions due to surrounding molecules or ions, will be accompanied by significant energy shifts in the spectra [1]. This allows one to better understand environment effects, and more easily characterize quantities which are central to the way of thinking of chemists, such as the assignment of oxidation states [2, 3], hybridization [4] or the degree of covalency in bonding [5].

In Resonant Inelastic X-ray Scattering (RIXS) the excitation from core orbitals to low-lying unoccupied orbitals is followed by emission of a photon, due to the transition of an electron from an occupied orbital to fill the hole left by the electron initially excited. RIXS can therefore provide correlations between different cores in the molecule, making it more effective in providing information on bonding on the species ground state wavefunction than ore, more widely used core spectroscopies are X-ray absorption spectroscopy (XAS), including the near-edge (XANES) region, and X-ray emission spectroscopy (XES) [6, 7].

It is not possible, however, to interpret the results from experiments with any such techniques without sound theoretical models. The latter require treatment of relativistic effects (due to the important spin-orbit coupling in the core region for even light elements), electron correlation and long-range (environment) effects.

The goal of this project is therefore to develop new theoretical tools that allow us to simulate RIXS spectra for molecules containing atoms across the periodic table, with a special interest in the actinides. These tools will be based upon the relativistic equation of motion (EOM-CC) framework [8], and will take into account environment effects (solvent, crystal etc.) through quantum embedding methods such as frozen density embedding (FDE) [9], which enable us to reduce the calculation's cost while retaining a quantum mechanical treatment for the whole system (CC-in-DFT embedding) [10]. These developments will be carried out in the DIRAC [11] and PyADF [12] programs.

[1] X Kong et al., The Journal of Physical Chemistry Letters 2017, 8, 4757
[2] B Kosog et al., Inorganic Chemistry 2012, 51, 7490
[3] ES Ilton, PS Bagus, Surface and Interface Analysis 2011, 43, 1549
[4] RD dos Reis et al., Nature Communications, 2017, 8, 1203
[5] Baker et al., Coordination Chemistry Reviews 2017, 345, 182
[6] K Kunnus et al., Chemical Physics Letters 2017, 669, 196
[7] T Vitova et al., Nature Communications 2017, 8, 1
[8] A Shee, T Saue, L Visscher, ASP Gomes, The Journal of Chemical Physics 2018, 149, 174113

Work Context

This thesis is part of the ANR-DFG project CompRIXS, involving a collaboration between our group and that of Prof. Christoph JACOB (TU Braunschweig), which focuses on the development of new ab initio electronic structure methods coupling different simulation scales.

The successful candidate will have a solid working knowledge in programming and in at least one of the more widely languages used in scientific programming (C /C++/Fortran/Python); a background on either computer science or electronic structure theory; solid communication skills (verbal/written); Ability/willingness to work in a collaborative setting. Education level: master or engineering school. Language: English and/or French.

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