CO和CO2 在UO2 (111)表面吸附和解离的第一性原理和分子动力学研究

First-Principles and ab-initio Molecular Dynamics Simula-tion Research on Adsorption and Dissociation of CO and CO2 Molecules on UO2 (111) Slab

摘要:

基于密度泛函理论（DFT）的第一性原理计算，在计算中加入Hubbard项进行校正，探究了CO和CO₂分子在UO₂ (111)表面的吸附和解离，分析了不同构型下的静态和动态吸附机理，吸附位点包括顶位、空位、桥位。在静态计算中，探究了吸附过程中多种吸附参数的变化，如吸附构型、吸附能、电荷转移等。利用第一性原理分子动力学（AIMD），探究了特定构型下CO₂分子的解离过程及差分电荷密度变化。结果表明，CO分子的吸附可分为2种类型：（1）自发吸附，包括化学和物理吸附；（2）非自发吸附。CO₂分子的吸附仅表现为自发吸附的化学吸附及非自发吸附，无物理吸附。CO和CO₂分子的最优吸附构型均为短桥位垂直（B-short-Ver）吸附。此外，0 K下CO₂分子在UO₂ (111)表面的B-short-Ver和长桥位垂直吸附构型吸附后会自发解离。AIMD模拟结果表明，这2种构型在300 K下均发生解离。

Abstract:

The adsorption and dissociation of CO and CO₂ molecules on UO₂ (111) slab were investigated by the first-principles calculations based on density functional theory with the addition of Hubbard term for calculation correction. Different static and dynamic adsorption mechanisms under different configurations were analyzed, and the adsorption sites included top, hollow, and bridge sites. In the static calculations, the variation of adsorption parameters, such as adsorption configuration, adsorption energy, and charge transfer, during adsorption process was investigated. ab-initio molecular dynamics (AIMD) was employed to study the dissociation process of CO₂ molecules and the changes in charge density difference. Results show that the adsorption of CO molecules can be categorized into two types: (1) stable adsorption, including chemical and physical adsorptions; (2) unstable adsorption. The adsorption types of CO₂ on UO₂ (111) slab only include the chemical adsorption of stable adsorption and unstable adsorption. No physical adsorption exists. The optimal configuration for the adsorption of both CO and CO₂ molecules is short-bridge vertical (B-short-Ver) adsorption. Additionally, at 0 K, the CO₂ molecules at the configurations related to B-short-Ver adsorption and long-bridge vertical adsorption on UO₂ (111) slab spontaneously dissociate after adsorption. AIMD simulation results show that both configurations dissociate at 300 K.