First principles determination of the crystal structures, vibrational spectra and mechanical and thermodynamic properties of uranyl minerals

Le prochain présentateur sera Francisco Colmenero, post doctorant au GET dont la présentation s’intitule First principles determination of the crystal structures, vibrational spectra and mechanical and thermodynamic properties of uranyl minerals. 

Résumé:

With the advent of increased computer capacities, improved computational resources and easier access to large scale computer facilities, the use of density functional theory methods has become nowadays a frequently used and highly successful approach for the research of solid-state materials. However, the study of solid materials containing heavy elements such as lanthanide and actinide elements is very complex due to the large size of these atoms and the requirement of including relativistic effects. These features impose the availability of large computational resources and the use of high-quality relativistic pseudopotentials for the description of the electrons localized in the inner shells of these atoms. The important case of the description of uranyl containing materials and their properties has been faced recently.

The study of these materials is very important in the energetic and environmental disciplines. Uranyl containing materials are fundamental components of the paragenetic sequence of secondary phases that results from the weathering of uraninite ore deposits and are also prominent phases appearing from the alteration of the spent nuclear fuel. The development of a new norm-conserving relativistic pseudopotential for uranium, the use of energy density functionals specific for solids and the inclusion of empirical dispersion corrections for describing the long-range interactions present in the structures of these materials have allowed the study of the properties of these materials with an unprecedent accuracy level. This feature is very relevant because these methods provide a safe, accurate and cheap manner of obtaining these properties for uranium containing materials which are highly radiotoxic, and their experimental studies demand a careful handling of the samples used.

In this seminar, the results of recent applications of theoretical solid-state methods based on density functional theory using plane waves and pseudopotentials to the determination of the crystal structures, vibrational spectra and mechanical and thermodynamic properties of uranyl minerals are reviewed. In the seminar, special emphasis will be given to the computation of thermodynamic functions. The knowledge of these functions is indispensable to model the dynamical behavior of nuclear materials under diverse geochemical conditions. The theoretical methods provide a deep understanding of the thermodynamic stability of these mineral phases and represent a powerful predictive tool to determine their thermodynamic properties.