| AVS 64th International Symposium & Exhibition | |
| Actinides and Rare Earths Focus Topic | Tuesday Sessions |
| Session AC+MI+SA+SU-TuA |
| Session: | Actinide and Rare Earth Theory |
| Presenter: | Valérie Vallet, CNRS / University of Lille, France |
| Authors: | V. Vallet, CNRS / University of Lille, France S. Kervazo, CNRS / University of Lille, France F. Réal, University of Lille, France A. Severo Pereira Gomes, CNRS / University of Lille, France F. Virot, IRSN, France |
| Correspondent: | Click to Email |
Actinide-containing complexes present formidable challenges for electronic structure methods due to the large number of degenerate or quasi-degenerate electronic states arising from partially occupied 5f and 6d shells. In particular, we focus our study here on volatile forms of plutonium such as PuO2, PuO3 or PuO2(OH)2, for which spectroscopic and thermodynamics properties are of interest.
To attain an accuracy comparable to that of experiments, highly accurate calculations including static and dynamic correlation effects as well as relativistic effects are required. Conventional multi-reference methods, however, can treat active spaces that are often at the upper limit of what is required for a proper treatment of species with complex electronic structures and large number of valence orbitals involved in chemical bonds, leaving no room for verifying their suitability.
In this work, we address first the issue of properly defining the active spaces in such calculations, and introduce a protocol to determine optimal active spaces based on the use of the Density Matrix Renormalization Group algorithm and concepts of quantum information theory.1
The guidance offered by this protocol allows us to define the suitable active space to compute the electronic structures
and the nature of the ground states with the desired accuracy, i.e. the clear multi-reference character of the wave-function of those compounds requires that the energies of formation to be computed with multi-configurational quantum chemical methods like CASSCF and CASPT2 and with spin-orbit interaction, treated here a posteriori with the state-interaction RASSI method. Specifically, our results illustrate the complex multi-configurational character of PuO3. The computed thermodynamics quantities reach a high accuracy allowing us to predict the composition of the released volatile products.