X-Ray Absorption Near Edge Spectroscopy for warm dense matter

Contexte :

The study of Warm Dense Matter (WDM) is a challenging field that is at the crossroads between condensed matter and plasma physics. XANES (X-ray Absorption Near Edge Structure) is a standard technique in condensed matter physics measurements which brings valuable information on electronic and ionic structure. This technique was recently extended to WDM regime. We showed (both theoretically and experimentally) that a precise description of X-ray absorption spectrum is a key diagnostic to follow the complex mechanism of phase transition. XANES absorption are computed using Density Functional Theory combined within the framework of Projected Augmented-Wave and linear response theory. This description makes use of frozen core approximation which severely limits the description for extreme pressure conditions (~100GPa and above). The challenge is now to go beyond the frozen core approximation keeping in mind that an all electrons calculation is numerically out of reach for this extreme conditions.

Objectif :

The position of the edge in the absorption spectrum is connected to the energy difference between the DOS and the core orbital. Both undergo variations with temperature and density that we have to take into account to describe a possible energy shift of the absorption features when modifying the thermodynamical conditions. This is mandatory to be able to compare theoretical and experimental spectra. This is challenging using PAW and frozen core approximation. One promising possibility is to make possible the relaxation of the core orbitals consistently with the valence electrons.
During this post-doc, the candidate will have to run DFT based molecular dynamics simulations on massively parallel computers to obtain the properties of metals in extreme pressure (T>10000K) and temperature (P>100GPa). Implementation will be necessary to improve the description of XANES spectra for this extreme condition. All implementation and calculation will be done with ABINIT code. All this work will be done with a close interaction with experimental teams.

CENTRE

DAM – Île-de-France
Bruyères-le-Châtel – 91297 Arpajon
01-69-26-40-00

CONTACTS

RECOULES Vanina
vanina.recoules@cea.fr
TORRENT Marc
marc.torrent@cea.fr