On the Multi-Reference Nature of Plutonium Oxides: PuO${}_2^{2+}$, PuO${}_2$, PuO${}_3$ and PuO${}_2$(OH)${}_2$

Abstract

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. Conventional multi-reference methods 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, leaving no room for verifying their suitability. In this work we address 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. We apply the protocol to elucidate the electronic structure and bonding mechanism of volatile plutonium oxides (PuO${}_3$ and PuO${}_2$(OH)${}_2$), species associated with nuclear safety issues for which little is known about the electronic structure and energetics. We show how, within a scalar relativistic framework, orbital-pair correlations can be used to guide the definition of optimal active spaces which provide an accurate description of static/non-dynamic electron correlation, as well as to analyse the chemical bonding beyond a simple orbital model. From this bonding analysis we are able to show that the addition of oxo- or hydroxo-groups to the plutonium dioxide species considerably changes the pi-bonding mechanism with respect to the bare triatomics, resulting in bent structures with considerable multi-reference character.

12 pages, 5 figures

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• The density matrix renormalization group for ab initio quantum chemistry
• Entanglement Measures for Single- and Multi-Reference Correlation Effects
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Cited by in corpus (11)

• Pythonic Black-box Electronic Structure Tool (PyBEST). An open-source Python platform for electronic structure calculations at the interface between chemistry and physics
• Orbital entanglement and correlation from pCCD-tailored Coupled Cluster wave functions
• Quantum Information-Assisted Complete Active Space Optimization (QICAS)
• Analysis of Electron Correlation Effects in Strongly Correlated Systems (${\mathrm{N}}_2$ and ${\mathrm{N}}_2^{+}$) by applying DMRG and Quantum Information Theory
• A configuration interaction correction on top of pair coupled cluster doubles
• Accurate Predictions of Volatile Plutonium Thermodynamic Properties
• Elucidating cation--cation interactions in neptunyl dications using multireference ab initio theory
• Electron correlation effects of the ThO and ThS molecules in the spinor basis. A relativistic coupled cluster study of ground and excited states properties
• New Strategies in Modeling Electronic Structures and Properties with Applications to Actinides
• Delving into the Catalytic Mechanism of Molybdenum Cofactors: A Novel Coupled Cluster Study
• Quantum information theory on sparse wavefunctions and applications for Quantum Chemistry