O与O_2在Au团簇上吸附的密度泛函理论研究

Density Functional Theory Study of Atomic and Molecular Oxygen Adsorption on Au Clusters

采用基于密度泛函理论(DFT)的Dmol3程序系统研究了O原子与O2在Au19与Au20团簇上的吸附反应行为.结果表明:O在Au19团簇顶端洞位上的吸附较Au20强;在侧桥位吸附强度相近.O与O2在带负电Au团簇上吸附较强,在正电团簇吸附较弱.从O―O键长看,当金团簇带负电时,O―O键长较长,中性团簇次之,正电团簇中O―O键长较短,因而O2活化程度依次减弱.电荷布居分析表明,Au团簇带负电时,O与O2得电子数较中性团簇多,而团簇带正电时,得电子数较少.差分电荷密度(CDD)表明,O2与Au团簇作用时,金团簇失电子,O2的π*轨道得电子,使O―O键活化.O2在Au-19团簇上解离反应活化能为1.33eV,较中性团簇低0.53eV;而在Au+19上活化能为2.27eV,较中性团簇高0.41eV,这与O2在不同电性Au19团簇O―O键活化规律相一致.

The adsorption behaviors of O and O2 on charged and neutral Au19 and Au20 clusters were systematically investigated by density functional theory （DFT） with Dmol3 program. Our results indicate that the adsorption energies of O on the hollow sites of Au19 are higher than those on Au20; while those on the side-bridge sites of the Au19 and Au20 clusters are similar. For negatively charged clusters, the adsorption energies of O and O2 are higher than those for neutral and positive clusters. The O―O bond lengths of the adsorbed O2 on the Au19 and Au20 clusters with different charges show a similar trend to the adsorption energy, that is, the O―O bond lengths on Au-19 are longer than those on the Au19 and Au＋ 19 clusters. Population analysis shows that more electrons transfer to the adsorbed O and O2 from the Au-19 and Au-20 clusters, which indicates stronger interactions compared with the neutral or positive clusters. Charge density difference （CDD） analysis for O2 on the Au19 and Au20 clusters suggests that electrons of the Au19 and Au20 clusters transfer to the π orbital of O2, upon which the O―O bonds are activated. The dissociation reaction barrier of O2 on Au-19 is 1.33 eV, which is lower than those on Au19 （1.86 eV） and Au＋ 19 （2.27 eV）.