甲硫醇在Cu(111)表面的解离吸附: 密度泛函理论研究

采用基于密度泛函理论的第一性原理方法和平板模型研究了CH₃SH分子在Cu(111)表面的吸附反应.系统地计算了S原子在不同位置以不同方式吸附的一系列构型, 第一次得到未解离的CH₃SH分子在Cu(111)表面顶位上的稳定吸附构型,该构型吸附属于弱的化学吸附, 吸附能为0.39 eV. 计算同时发现在热力学上解离结构比未解离结构更加稳定. 解离的CH₃S吸附在桥位和中空位之间, 吸附能为0.75-0.77 eV. 计算分析了未解离吸附到解离吸附的两条反应路径, 最小能量路径的能垒为0.57 eV. 计算结果还表明S―H键断裂后的H原子并不是以H₂分子的形式从表面解吸附而是以与表面成键的形式存在. 通过比较S原子在独立的CH₃SH分子和吸附状态下的局域态密度, 发现S―H键断裂后S原子和表面的键合强于未断裂时S原子和表面的键合.

Dissociative Adsorption of Methanethiol on Cu(111) Surface: a Density Functional Theory Study

The interaction of methanethiol (CH₃SH) molecules with the Cu(111) surface was investigated using a first-principles method based on density functional theory, and a slab model. A series of possible adsorption configurations constructed using S atoms on different sites with different tilt angles were studied. It was found for the first time that the non-dissociative molecular adsorption of CH₃SH on the Cu(111) surface with the S atom sitting on the top site belongs to the weak chemisorption, and the adsorption energy is 0.39 eV. After the dissociation of the S―H bond, the S atom is located at the bridge site, with a small shift toward the hollow site. The dissociative adsorption structure is thermodynamically more stable than the intact one, and the adsorption energy is 0.75-0.77 eV. Two reaction pathways have been studied for the transition from non-dissociative adsorption to dissociative adsorption, and the activation energy barrier along the minimum energy path is 0.57 eV. The results of the calculations indicated that the released H atom prefers to form a bond with the copper surface, rather than desorbing in the H₂ molecular form. Comparing the local density of states of S atoms in the single CH₃SH, CH₃SH/Cu(111), and CH₃S/Cu(111) structures, we found that the bonding between the S atoms and the substrate is much stronger in the dissociated adsorption states.