Properties of the tetravalent actinide series in aqueous phase from a microscopic simulation automated engine

TL;DR

This study uses automated ab initio-based molecular dynamics simulations to explore the properties of tetravalent actinides in water, providing insights that complement experimental challenges and highlight trends across the series.

Contribution

First automated ab initio-based force field simulations for the entire tetravalent actinide series in water, enabling detailed analysis of their properties and trends.

Findings

Simulated actinide hydration structures match experimental data.

Properties of actinides vary progressively along the series, except for Am and Cm.

The modeling approach is robust and suitable for predictive studies.

Abstract

In the context of nuclear fuel recycling and environmental issues, the understanding of the properties of radio-elements with various approaches remains a challenge regarding their dangerousness. Moreover, experimentally, it is imperative to work at sufficiently high concentrations to reach the sensitivities of the analysis tools, which often leads to precipitation for some of them, and stabilizing of specific oxidation states of some actinides remains a challenge, thus making it difficult to extract general trends across the actinide series. Complementary to experiments, modelling can be used to unbiasedly probe the actinide's properties in aquatic environment and offers a predictive tool. We report the first molecular dynamics simulations based on homogeneously built force fields for the whole series of the tetravalent actinides in aqueous phase from $\mathrm{Th^{IV}}$ to $\mathrm{Bk^{IV}}$ and including $\mathrm{Pu^{IV}}$. The force fields used to model the interactions among the constituents include polarization and charge donation microscopic effects. They are built from an automated iterative \textit{ab initio} based engine, the core element of a future machine learning procedure devoted to generate accurate force fields. The comparison of our simulated hydrated actinide properties to available experimental data show the model robustness and the relevance of our parameter assignment engine. Moreover our simulated structural, dynamical and hydration free energy data show that, apart from $\mathrm{Am^{IV}}$ and $\mathrm{Cm^{IV}}$, the actinides properties change progressively along the series.