CE29 - Chimie : analyse, théorie, modélisation

Computation of Resonant Inelastic X-ray Scattering in the condensed phase across the whole periodic table – CompRIXS

Computation of Resonant Inelastic X-ray Scattering in the condensed phase across the whole periodic table

This project aims to devise and apply innovative theoretical approaches to simulate Resonant Inelastic X-ray Scattering (RIXS) spectra, whereby we accurately take into account relativistic effects (especially spin-orbit coupling) while at the same time treating electron correlation, relaxation, and environment effects.

Why and how to model environment effects on RIXS spectra

Processes involving the excitation or ionization of core electrons are very usefu for the characterization of matter in the microscopic scale: they are very selective with respect to the atomic center being probed, and very sensitive to the chemical environment surrounding this center. Experimental signals however cannot be interpreted without reliable theoretical models, such as those provided by (relativistic) correlated electronic structure methods. The latter generally computationally expensive, in particular for modeling syatems in complex environments (solvent etc) since the interaction between species of interest and such environments can significantly alter their spectral signatures.

We apply relativistic and non-relativistic electronic structure theory to simulate core spectra (XPS, XAS, RIXS), employing quantum embedding approaches to reduce computational cost while retaining a very good accuracy for the the simulation of the spectra of the species of interest.

The project has delivered to date : (1) a simple theoretical model and a computer implementation of it capable of efficiently simulating RIXS maps with molecular electronic structure tools; (2) a code capable of performing rt-TDDFT calculations that can take into account environment effects in valence and XAS spectra with projection-based embedding; (3) a code capable of performing relativistic rt-TDDFT calculations that can take into account environment effects in valence and XAS spectra, with frozen density embedding; (4) highly accurate (coupled cluster) reference data on XPS and XAS spectra of glycine and uranyl complexes in the presence of an environment.

The project will pursue the development of quantum embedded real-time propagation approaches at different levels of theory (DFT and coupled cluster), that are capable of simulating core spectra in general and RIXS spectra in particular.

M. De Santis, L. Belpassi, C.R. Jacob, A.S.P Gomes, F. Tarantelli, L. Visscher, L. Storchi, J. Chem. Theory Comput. 2020, 16, 5695. 10.1021/acs.jctc.0c00603

L Halbert, M.L. Vidal, A. Shee, S. Coriani, A.S.P. Gomes, J. Chem. Theory. Comput. 2021, 17, 3583. 10.1021/acs.jctc.0c01203

J. V. Pototschnig, A. Papadopoulos, D.I. Lyakh, M Repisky, L. Halbert, A.S.P. Gomes, H.J.Aa. Jensen, L. Visscher, J. Chem. Theory. Comput. 2021, 17, 5509. 10.1021/acs.jctc.1c00260

J. V. Pototschnig, K.G. Dyall,. L. Visscher , A.S.P. Gomes,. Phys. Chem. Chem. Phys., 2021.10.1039/D1CP03701C

Resonant Inelastic X-ray Scattering (RIXS) allows for detailed insights into the electronic structure of molecular species. Owing to the installation of modern synchrotron radiation sources, it has seen rapid development in recent years. RIXS and other X-ray spectroscopic techniques, however, are alike in that it is very difficult to interpret their spectra without aid from theory. By combining the expertise of the German and French partners, we aim at addressing the accurate calculation of RIXS spectra in light elements, in transition metal complexes, and heavy element systems in the condensed phase. To this end, we propose the development of real-time response methods based on density-functional theory (DFT) and on relativistic equation-of-motion coupled cluster theory for the calculation of RIXS spectra. To account for solvent and crystal environments, these approaches will be combined with quantum-chemical embedding methods based on the frozen-density embedding formalism. These novel computational approaches will be applied to experimentally relevant test cases featuring elements across the whole periodic table, namely amino acids in solution, iron complexes, and uranyl species in the condensed phase.

Project coordination

André SEVERO PEREIRA GOMES (Physique des lasers, atomes et molécules)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

TC-TUBS Technische Universität Braunschweig / Theoretical Chemistry
PhLAM Physique des lasers, atomes et molécules

Help of the ANR 193,233 euros
Beginning and duration of the scientific project: April 2020 - 36 Months

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