Cu(001)表面CO吸附单层结构和电子态的第一性原理研究

用密度泛函理论(DFT)研究了Cu(001)表面CO吸附单层的表面性质. 总能计算结果表明, 顶位结构总能最低, 相应位置的CO分子吸附能最大. 谷位吸附结构的衬底原子层间距相对于清洁表面的膨胀量约为10%, 从而导致了谷位吸附的不稳定性. 在顶位、桥位和谷位三个吸附结构中, C和Cu原子之间的距离dC-Cu分别为0.1868、0.1975和0.2231 nm, 对应的CO分子键长为0.1154、0.1165 和0.1175 nm. 计算了CO分子的态密度(DOS). 结果表明, 衬底与分子的作用主要是分子和金属轨道的杂化. 在吸附过程中, 电荷主要从碳原子的s轨道向p轨道转移. 在顶位、桥位和谷位吸附结构中, 每个碳原子内电荷的转移量分别为0.45e、0.54e 和0.55e. 衬底向吸附分子的电荷转移量不大, CO 吸附分子层为一绝缘层.

First-Principle Calculations on the Atomic Geometry and Electronic States of CO Monolayer on Cu(001) Surface

First-principle calculations were performed on the geometric structure and adsorption properties of CO monolayer on Cu(001) surface by using USPP and FLAPWmethods. Relaxed geometry structure suggested that top was the most stable site. The distance between C and Cu atoms was about 0.1868 nm on top site, compared with 0.1975 nm on bridge sites and 0.2231 nm on hollow sites. The bond length of CO molecules on top, bridge and hollow sites were estimated to be 0.1154, 0.1165 and 0.1175 nm, respectively. From the structure of adsorbed surface, it was found that the bond length of COwas enlarged by the nearest copper atoms. PDOS (partial orbital of density of state) of COshowed that the interaction between adsorbent and adsorbate was mainly induced by the hybridization of molecule 5σ orbital and copper 3d orbital. The hybridization was mainly induced by the symmetry of orbital and sites. The result of orbital charge indicated that the s orbital charge of carbons reduced and the p orbital charge of carbons increased, when CO molecules were adsorbed on the top sites. At last, the work functions for three adsorbed surfaces were investigated, which were calculated to be 5.51 eV on top, 6.00 eV on bridge, and 6.23 eV on hollow, in contrast to 4.57 eV in clean surface. The work function and DOS indicated that CO layer was insulating.