CO2 在 δ-Pu(100)表面吸附行为的第一性原理研究

Study on Adsorption Behavior of CO2 on the δ-Pu(100) Sur-face Based on First-principles

摘要:

结合密度泛函理论框架内的周期性平板模型，运用第一性原理计算方法研究了CO₂在δ-Pu(100)表面的吸附行为。结果表明，CO₂分子以C端向下和C-Pu、O-Pu多键结合的方式吸附在δ-Pu(100)表面。吸附类型属于强化学吸附，最稳定的吸附构型是H₁-C₄O₄，此时吸附能为-6.430 eV，吸附稳定性顺序为穴位>桥位>顶位。CO₂分子主要和表面Pu原子反应，而与其它3层Pu原子的反应较弱。更多的电子向CO₂ 2π_u轨道转移有利于C-O键的弯曲和活化。此外，CO₂分子和Pu原子之间的化学键主要是离子态，反应机理是CO₂的C 2s、C 2p、O 2s 和O 2p轨道与Pu 6p、Pu 6d、Pu 5f轨道发生了重叠杂化作用，产生了新的键结构。H₁-C₄O₄构型的功函数变化最小，表明其它电子容易从该构型表面逃逸，且需要的能量最小。

Abstract:

A first-principles calculation was applied to study the adsorption behavior of CO₂ on δ-Pu(100) surface using a slab model within the framework of density functional theory. Results demonstrate that CO₂ molecules are adsorbed on δ-Pu(100) surface at C-terminated bent state by multi-bond binding of C-Pu and O-Pu. The adsorption type belongs to strong chemical adsorption and the most stable adsorption configuration is H₁-C₄O₄ with the adsorption energy of -6.430 eV. The adsorption stability order is hollow site>bridge site>top site. CO₂ molecule mainly interacts with Pu surface atoms, while the interaction with other three Pu atoms is weak. The transfer of more electrons to the CO₂ 2π_u orbital is beneficial to the bending and activation of C-O bonds. Moreover, the chemical bonding between Pu atoms and CO₂ molecule is mainly ionic state and the reaction mechanism is that the C 2s, C 2p, O 2s and O 2p orbitals of CO₂ molecule hybrid with Pu 6p, Pu 6d and Pu 5f orbitals, resulting in a new bond structure. The work function of the H₁-C₄O₄ site changes the least, indicating that other electrons readily escape from the metal surface and the required energy is the smallest.