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

Subject Area Theoretical Chemistry: Electronic Structure, Dynamics, Simulation
Term from 2019 to 2023
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 431402644
 
Final Report Year 2024

Final Report Abstract

Advanced industrial societies rely heavily upon heavy elements in domains such as catalysis (transition metals), consumer electronics and renewable energy (lanthanides), or nuclear energy production (actinides). To understand current materials and develop new ones, it is necessary to understand their behavior (particularly that of their electrons) at the molecular scale. This can be done experimentally by exploring their interaction with light (spectroscopy). Spectroscopic methods probing the electrons closest to the nuclei (core electrons) with X-rays provide very specific information about the chemical environment surrounding specific atoms. Experiments are, however, very difficult to interpret without reliable theoretical models. The goal of the CompRIXS project was to develop theoretical models to simulate resonant inelastic X-ray scattering (RIXS) with the same accuracy for all elements across the periodic table. This differentiates it from most other approaches that do not properly treat physical processes of fundamental importance for heavy elements (relativistic effects). The CompRIXS project involved the development of so-called electronic structure methods, through with the time-(in)dependent Schrödinger or Dirac equation for the electrons can be solved. We have worked with three families of methods: those based on density functional theory (DFT), which are computationally very efficient but only moderately accurate; those based on the relativistic coupled cluster theory (RCC), which are very accurate but computationally very expensive; and quantum embedding (QE) approaches, where RCC and DFT are combined, so that the RCC approach can proved a very accurate description for the most important part of the system-the light absorbing part-while the rest of the system surrounding the absorbing center is described with DFT. With that, the QE approach allows for a computationally cost-effective, fully quantum mechanical treatment of very complicated systems. This, in turn, allows one to consider more realistic models of complex chemical systems. CompRIXS has developed (a) approximate DFT-based methods to calculate RIXS maps with (non-)relativistic Hamiltonians; (b) QE real-time TDDFT methods that can describe the coupling of the response of active sub-systems and its environment; and (c) relativistic CC response theory methods that can describe one- and two-photon processes. These computational tools are now being used to simulate XAS and RIXS of actinide complexes. Furthermore, the computer implementation of the methods developed in CompRIXS have been made available as open-source software and have been included as integral parts of widely used open-source software such as DIRAC and PyADF.

Link to the final report

https://doi.org/10.24355/dbbs.084-202503191103-0

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