The aim of this project is to describe the solvation of actinoids and lanthanoids at the microscopic level. To this end, novel molecular dynamics simulations will be coupled to DFT-based studies and experiments. Some of the experiments will be done in the context of this project in order to go beyond available experimental data from the literature. All simulations will be done within this project and they will be useful to better interpret these. Knowledge of the chemical properties of actinoids (and indirectly also of lanthanoids) has a strong societal impact for their use in nuclear energy processes. While lanthanoids are present mainly at oxidation state III, actinoids have several oxidation states, especially the first elements in the series, often forming in water oxocations. In our project, we will focus on oxidation state III and some An(IV). Thus we can shed light on analogies and differences between the two series bare cations. In particular, we will treat solvation in water, forming aqueous complexes with carbonates and silicates for An(III) and Ln(III), and in two different solvents, dimethylformamide (DMF) and dimethylsulfoxide (DMSO) for An(III) and (IV) and Ln(III). We will develop polarizable classical interaction potentials, using the same approach developed by us for Ln(III) hydration, that will be coupled with different experimental techniques: X-ray absorption spectroscopy (and EXAFS in particular), providing structural properties and time-resolved laser induced fluorescence spectroscopy (TRLFS) aimed to understand complexation with silicates. These last will be coupled to electrospray mass spectrometry (ESI-MS) to solve the question of nature of ligands, i.e. mono or poly silicates. Our project is divided in three tasks where different ligands will be investigated and a fourth task where, making the use of DFT-based dynamics and using results of other tasks, we will be able to understand the analogies and differences between Ln(III) and An(III) in solution. In particular in task 1 we will investigate An(III) hydration with classical molecular dynamics. In task 2 we will pass to aqueous complexes of An(III) and Ln(III) with carbonates and silicates by means of classical molecular dynamics and TRLFS experiments for silicates. In task 3 we will understand solvation behavior of An(III), An(IV) and Ln(III) in DMF and DMSO by coupling simulations with EXAFS experiments, providing also information on An(IV) properties in non-aqueous solvents. In parallel, starting after the achievement of task 1, we will develop task 4 that will provide us the microscopical basis of An(III)/Ln(III) analogies and differences. Further, by means of DFT-based simulations we will have an additional validation of classical force fields and we will give the basis for a possible employment of these methods to actinoids and lanthanoids reactivity. Within this project, we will put together young researchers of both academical institutions and CEA on a subject that has fundamental key questions but also a connection with the field of nuclear waste management. The project coordinator, R.Spezia (CNRS, LAMBE) has experience on solvation by means of both classical and DFT-based dynamics. Within this project he will be able to build up a team on very heavy metal ions solvation that can be a reference in Europe, since it will put together experiments (that on actinoids are limited to few centers) with theoretical developments. R.Vuilleumier (CNRS, PASTEUR) will provide his competences in DFT-based dynamics. T.Vercouter (CEA, Saclay) works on complexation reactions for actinoids with environmentally-relevant inorganic ligands by spectroscopic and spectrometric techniques and he will carry out TRLFS experiments on Ln(III) and An(III) interacting with silicates in water. C.Fillaux and C.Den Auwer (CEA, Marcoule) will be the EXAFS experimentalists needed for the team, since they are experts on actinoids XAS.