Ab initio structure and energetics of Pu(OH)4 and Pu(OH)4(H2O)n clusters: Comparison between density functional and multi-reference theories

► Bare and hydrated Pu(IV) hydroxide are studied using a range of a ab initio theories. ► Multi-reference effects do not appear to be significant for ground-state properties. ► PBE and PBE0 can yield qualitative differences compared to unrestricted MP2. ► We derive an ab initio parameterization of the DFT + U apprich for aqueous Pu(IV). ► A value of U − J = 5.5 eV is proposed for DFT + U simulations of Pu(OH)4 in liquid water.