Actinoid tetroxide molecules AnO₄ (An = Ac – Cm) are investigated with the ab initio density matrix renormalization group (DMRG) approach. Natural orbital shapes are used to read out the oxidation state (OS) of the f-elements, and the atomic orbital energies and radii are used to explain the trends. The highest OSs reveal a “volcano”-type variation: For An = Ac – Np, the OSs are equal to the number of available valence electrons, that is, Ac^III, Th^IV, Pa^V, U^VI, and Np^VII. Starting with plutonium as the turning point, the highest OSs in the most stable AnO₄ isomers then decrease as Pu^V, Am^V, and Cm^III, indicating that the 5f-electrons are hard to be fully oxidized off from Pu onward. The variations are related to the actinoid contraction and to the 5f-covalency characteristics. Combined with previous work on OSs, we review their general trends throughout the periodic table, providing fundamental understanding of OS-relevant phenomena.

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关于 AnO4 分子中锕系元素的最高氧化态 (An = Ac – Cm)：DMRG-CASSCF 研究

使用从头算密度矩阵重整化组 (DMRG) 方法研究四氧化锕类分子 AnO _{4 (An = Ac – Cm)。}自然轨道形状用于读出 f 元素的氧化态 (OS)，原子轨道能量和半径用于解释趋势。最高的 OS 显示出“火山”型变化：对于 An = Ac – Np，OS 等于可用价电子的数量，即 Ac ^III、Th ^IV、Pa ^V、U ^VI和 Np ^VII。以钚作为转折点开始，最稳定的 AnO ₄异构体中的最高 OS 随 Pu ^V、Am ^V和 Cm而降低^III，表明 5f 电子很难从 Pu 开始完全氧化掉。这些变化与锕系收缩和 5f-共价特性有关。结合之前关于操作系统的工作，我们回顾了它们在整个元素周期表中的一般趋势，提供了对操作系统相关现象的基本理解。