Nb(100)表面吸附氮气的第一性原理研究

Nitrogen adsorption on Nb(100) surface by using First-principles investigation

为研究氮气在Nb(100)表面吸附过程中的物理机制,采用密度泛函理论和第一性原理方法对Nb(100)表面吸附氮气的功函数、几何结构、吸附能、电子结构和振动频率等性质进行研究。计算结果表明:当分子覆盖度为1.0 ML时,垂直的氮气易于吸附在Nb(100)表面的顶位;当分子覆盖度为0.5 ML时,桥位是氮气吸附于表面的最稳吸附位;当分子覆盖度为0.25 ML时,氮气则基本垂直吸附在顶位。分波态密度的研究发现,Nb(100)表面和氮气之间的相互作用主要通过Nb原子的d轨道与N原子的px,py轨道间的杂化。吸附分子中两氮原子间的振动频率强烈地依赖于其吸附结构,垂直吸附分子的N—N键的振动频率强于倾斜和平行吸附分子的。垂直吸附桥位和顶位的氮分子间原子振动频率分别是1 872～2 068 cm-1和2 173～2 204 cm-1。

In order to study the physical mechanism of N2 adsorption on Nb（100） surface, the density functional theory calculations and first principle investigation were performed to investigate the work function, structural properties, adsorption energies, electronic structures, and surface vibrational modes of N2 on Nb（100） surface. Results show that the upright N2 prefers to be absorbed on top sites at 1.0 ML coverage, while the bridge site is the most favorable site at 0.5 ML. At 0.25 ML, vertical N2 is absorbed on top sites steadily. Further analyses based on partial density of states reveal that the essential interaction between N2 and metal substrate is the hybridization of N Px, Pyorbital and the d-bands of surface niobium atoms. The frequencies of N2 exhibit the expected strong adsorption structure dependence： N2 molecules adsorbed in the vertical structures vibrate faster than those in parallel and tilted structures. In the modes of upright N2 on top and bridge sites, the adsorption ranges are 2173-2204 cm-l and 1 872 -2 068 cm-1, respectively.