W_n(n=1—6)团簇吸附CO的密度泛函研究

Density functional theory study of the adsorption of CO on W_n(n=1—6) clusters

采用密度泛函理论(density functional theory,DFT)在B3LYP/LANL2DZ基组水平上对钨团簇吸附CO分子进行了系统研究.结果表明,WnCO团簇的基态结构是在Wn团簇中性或阴离子基态结构的基础上吸附CO生长而成;CO的吸附以端位吸附为主,桥位吸附为辅;CO分子在Wn团簇表面发生的是非解离性吸附.与优化的CO键长(0.116nm)相比,吸附后C-O键长变长(0.120—0.123nm),表明吸附后C-O键被削弱,CO分子被活化了.稳定性分析表明,在所研究的团簇中,W3CO和W5CO团簇的稳定性较强;自然键轨道(NBO)分析表明,W原子与CO分子相互作用的本质是CO分子内的杂化轨道与W原子6s,5d,6p和6d轨道相互作用的结果.

CO molecules adsorbed on the Wn clusters are systematically investigated by using density functional theory at the B3LYP/LANL2DZ level.The result indicates that the ground state structures of WnCO clusters are generated when CO molecules are adsorbed on Wn clusters or anionic cluster. We find that among the molecular adsorption states exists mainly the form of end- on type geometry, and that the bridge site adsorption type geometry plays a supplementary role. On the face, the adsorption is a non-dissociative adsorption. The CO bond length increases 0.120-0.123 nm in WnCO cluster （compared with 0.116 nm in free CO molecule）, which demonstrates that the CO molecules are activated. The stability analysis shows that W3CO and W5CO clusters are more stable than other clusters; natural bond orbital （NBO） analysis indicate that the interaction between W atom and CO molecule is primarily contributed by hybridization of molecular orbits within CO and 6s, 5d, 6p and 6d orbits of W atoms.