Excited electronic states in the GW Approximation coupled to the Projector Augmented-Wave Approach
This project aims to address a major gap in ab initio calculations by enabling reliable simulations of excited electronic states (GW method) using the Projector Augmented-Wave (PAW) approach. These advances will be integrated into the open-source software ABINIT, a recognized international collaborative project. The GW approximation is considered the gold standard for determining electronic energy levels in condensed matter, correcting the underestimated band gap in DFT. The PAW method, on the other hand, offers precision and flexibility and is widely used for ground state and material response calculations.
However, the combined GW+PAW approach encounters difficulties in some well-identified cases (e.g., zinc oxide), with underlying reasons understood but not yet fully resolved. Low-energy excited states are well described, but high-energy states remain problematic. The current debate focuses on the need to perform complete (but computationally expensive) calculations, to neglect certain terms (with complex error control), or to modify the PAW method (at the cost of reduced efficiency).
The project aims to adapt the PAW formalism to the GW approach, to develop a fast and accurate numerical scheme, and to clarify the current, somewhat confusing situation. The CEA team is a leading developer of ABINIT for PAW and GW and will ensure access to large computing resources. The postdoctoral objectives include theoretical development, implementation in ABINIT, and improving electronic properties for realistic solid systems (surfaces, semiconductor junctions, etc.).
Atomic-Scale Study of Dislocation-Point Defect Interaction in UO2 Fuel
Uranium dioxide (UO2) is the primary fuel used in pressurized water reactors (PWRs). Under normal operating conditions and irradiation, the mechanical and microstructural behavior of UO2 evolves due to the accumulation of point defects (vacancies, interstitials, defect clusters) generated by nuclear fission events. These defects alter the thermo-mechanical behavior of the material, particularly through their interaction with dislocations, thereby influencing plasticity, stress relaxation, and ultimately, fuel integrity.
A detailed understanding of the elementary mechanisms governing these interactions is essential for improving the modeling of irradiated fuel mechanical behavior. In particular, the impact of point defects on dislocation mobility remains a key challenge in refining the constitutive laws used in the multi-scale simulation tools of the PLEIADES platform, which is dedicated to predicting fuel behavior under various operating conditions (nominal, transient, and accidental scenarios).
The objective of this study is therefore to analyze, at the atomic scale, the interactions between dislocations and point defects in UO2 in order to quantify their influence on the fundamental plasticity mechanisms. To this end, molecular dynamics calculations will be performed to investigate the effect of different types of point defects (e.g., Frenkel pairs) on dislocation mobility, considering key parameters such as temperature and applied stress. This work will enable the extraction of dislocation mobility laws in the presence of defects, which will serve as input data for micromechanical models used in larger-scale simulations, particularly those implemented in the PLEIADES platform.
Impact of Microstructure in Uranium Dioxide on Ballistic and Electronic Damage
During reactor irradiation, nuclear fuel pellets undergo microstructural changes. Beyond 40 GWd/tU, a High Burnup Structure (HBS) appears at the pellet periphery, where initial grains (~10 µm) fragment into sub-grains (~0.2 µm). In the pellet center, under high temperatures, weakly misoriented sub-grains also form. These changes result from energy loss by fission products, leading to defects such as dislocations and cavities. To study grain size effects on irradiation damage, nanostructured UO2 samples will be synthesized at JRC-K, using flash sintering for high-density pellets. Ion irradiation experiments will follow at JANNuS-Saclay and GSI, with structural characterizations via Raman spectroscopy, TEM, SEM-EBSD, and XRD. The postdoc project will take place at JRC-K, CEA Saclay, and CEA Cadarache under expert supervision.
Thermochemical and thermodynamic study of chloride molten salts
In today’s climate emergency, access to clean and cheap energy is more important than ever. Several ways have been envisaged for several years now, but a number of technological issues still need to be overcome before they can be put into practice, as they represent breakthroughts. Whether for energy storage than for fourth generation nuclear reactors, molten salt environment used as coolant and/or as fuel is highly corrosive requiring a complexe choice of structural materials.
The aim of this subject proposed in the Corrosion and Materials Behavior Section is to study in depth the chemical properties of different chloride molten salts : the basic ternary salt (NaCl-MgCl2-CeCl3) but also the corrosion/fission/activation products that can be produced (MxCly with M=Cr, Fe, Te, Nd, Ni, Mo,…). The activity coefficients and solubility limits of these metallic elements will be determined using various techniques such as electrochemistry and Knudsen cell mass spectrometry. If required, this study can be completed by the phase transition temperature and heat capacity measurements using differential scanning calorimetry.
2D materials electrical characterization for microelectronics
Future microelectronic components will be ever smaller and ever more energy-efficient. To meet this challenge, 2D materials are excellent candidates, thanks to their remarkable dimensions and electronic properties (high mobility of charge carriers, high light emission/absorption). What's more, they feature van der Waals (vdW) surfaces, i.e. no dangling bonds, enabling them to retain their properties even at very small dimensions (down to the monolayer). New 2D materials and vdW stacks with novel physical properties are being discovered every day. However, integrating them and measuring their performance in circuits remains an ongoing challenge, as their properties must be preserved during integration.
The aim of this post-doc is to develop components for qualifying 2D materials for microelectronic (RF transistor) and spintronic (magnetic memory) applications in horizontal configuration on silicon. A vertical measurement method has already been developed by CEA LETI. Building on these developments, the candidate will develop this measurement system and characterize various materials produced in MBE by CEA-IRIG. The work will involve transferring these layers onto chips, optimizing the electrical contacts and developing the in-plane electrical measurement chain.
Preparation and characterization of an oxide/oxide composite
Fiber-reinforced ceramic matrix composites (CMCs) are a class of materials that combine good specific mechanical properties (properties relative to their density) with resistance to high temperatures (> 1000 °C), even in oxidizing atmospheres. They are typically composed of a carbon or ceramic fiber reinforcement and a ceramic matrix (carbide or oxide.
The proposed study focuses on the development of a low-matrix oxide/oxide CMC with suitable dielectric, thermal, and mechanical properties.
This study will be conducted in collaboration with several laboratories at CEA Le Ripault.
Development of new Potassium-ion cells with high performances and low environmental impact
Lithium ion batteries are considered as the reference system in terms of energy density and cycle life and will play a key role in the energetic transition, especially concerning electric vehicles. However, such a technology involves the use of a large amount of critical elements and active materials are synthesised using energy intensive processes.
In this way, our team is developing a new Potassium-ion batteries technology with high performances but with a low environmental impact.
For this innovative and ambitious project, CEA-LITEN (one of the most important research institute in Europe) is looking for a talented post-doctoral researcher in material chemistry. The post-doctoral position is opened for a young researcher with a high scientific level, interested by valorising her/his results through different patents and/or scientific publications.
Influence of laser bandwidth and wavelength on laser plasma instabilities
As part of the Taranis project initiated by Thales and supported by BPI France and in collaboration with numerous scientific partners such as CEA/DAM, CELIA and LULI, work on target design and definition of the laser intended to energy production in direct drive will take place. A prerequisite for this work is to understand the laser-plasma interaction mechanisms that will occur when the laser is coupled with the target. These deleterious mechanisms for the success of fusion experiments can be regulated by the use of so-called “broadband” lasers. In addition, the choice of the laser wavelength used for the target design and the laser architecture must be defined. The objective of the postdoctoral position is to study the growth and evolution of these instabilities (Brillouin, Raman) in the presence of “broadband” lasers both from an experimental and simulation point of view, and thus to be able to define the laser conditions making it possible to reduce these parametric instabilities.
Separation microsystem coupled to mass spectrometry for on-line purification and characterisation of nuclear samples
The miniaturisation of analytical steps commonly carried out in laboratories offers many advantages and particularly in the nuclear sector, where the reduction of material consumption and waste production is of major interest. In this context, one of our laboratory’s focus area is the miniaturisation of analytical tools, particularly chromatographic separation techniques. The aim of this project is to reduce the scale of the purification steps of nuclear samples by solid phase extraction chromatography, prior to the analytical processes. Obtaining these miniaturised extraction devices is based on the in situ synthesis and anchoring of monoliths, in the channels of cyclic olefin copolymer (COC) microsystems. Since this material is chemically inert, COC functionalisation strategies are currently under development to covalently graft reactive sites on its surface, before locally anchoring actinide-specific monoliths in the micro-channels. The aim is to design and fabricate chromatographic extraction microsystems in COC, and to implement them for chemical purification and mass spectrometry measurements, both off-line and on-line.