Polarons generally affect adversely the photochemical and photophysical properties of transition metal oxides. However, the excited-state dynamics of polarons are not fully established to date and thus require an atomistic understanding. We focus on α-Fe₂O₃ with photoexcitation, electron injection, and heterovalent doping as the small polaron models, and conduct simulations of ab initio adiabatic molecular dynamics (AIMD) and nonadiabatic molecular dynamics (NA-MD). The elaborately designed AIMD simulations show that localization of electron at a single Fe site is an adiabatic and ultrafast process within sub-15 fs. Fe₂O₃ doping with an electron or a Si and Ti dopant forms a localized electron polaron while photoexcitation forms localized electron and hole polarons simultaneously, leading to diverse electron–hole recombination dynamics. NA-MD simulations demonstrate that recombination of an electron polaron created by doping with a delocalized hole at the valence band maximum of α-Fe₂O₃ takes place around 5 ps, while recombination between a pair of small electron and hole polarons in photoexcited Fe₂O₃ delays to about 110 ps owing to weak NA coupling and fast decoherence process. The ultrafast formation of small electron polarons in α-Fe₂O₃ impedes the accumulation of delocalized holes in the valence band that directly participate in water oxidation at photoanodes. The detrimental effect can be partially circumvented in photoexcited Fe₂O₃ for slowing electron–hole recombination despite polarons may retain low charge mobility. These findings provide a fundamental understanding of the excited-state dynamics of small electron polaron in α-Fe₂O₃ and may help design efficient transition metal oxides photoanodes.

极化子通常不利地影响过渡金属氧化物的光化学和光物理性质。然而，迄今为止，极化子的激发态动力学尚未完全建立，因此需要原子理解。我们专注于以光激发、电子注入和异价掺杂作为小极化子模型的α-Fe ₂ O ₃，并进行从头算绝热分子动力学（AIMD）和非绝热分子动力学（NA-MD）的模拟。精心设计的 AIMD 模拟表明，电子在单个 Fe 位点的定位是低于 15 fs 的绝热和超快过程。铁₂ O ₃掺杂电子或Si和Ti掺杂剂形成局域电子极化子，而光激发同时形成局域电子和空穴极化子，导致不同的电子-空穴复合动力学。_{NA-MD 模拟表明，通过在 α-Fe 2} O ₃的价带最大值处掺杂离域空穴而产生的电子极化子的复合发生在 5 ps 左右，而在光激发的 Fe 中一对小电子和空穴极化子之间的复合由于弱NA耦合和快速退相干过程，₂ O _{3延迟至约110 ps。α-Fe 2} O ₃中小电子极化子的超快形成阻碍价带中离域空穴的积累，这些空穴直接参与光阳极处的水氧化。_{尽管极化子可能保持低电荷迁移率，但在光激发的 Fe 2} O ₃中可以部分规避有害影响，以减缓电子-空穴复合。_{这些发现提供了对 α-Fe 2} O ₃中小电子极化子的激发态动力学的基本理解，并可能有助于设计高效的过渡金属氧化物光阳极。