NO在(Fe_2O_3)_n(2≤n≤6)团簇上吸附的密度泛函理论研究

Density functional study of NO adsorbed on(Fe_2O_3)_n(2≤n≤6) clusters

运用广义梯度密度泛函理论(GGA)的Pcrdew-Burke-Emrnerh(PBE)方法结合团簇模型,在双数值极化函数基组DNP下,研究了(Fe_2O_3)_n(2≤n≤6)团簇的性质和NO在其上的吸附。对于(Fe_2O_3)_n团簇通过对几何构型和性质的计算发现;(Fe_2O_3)_n团簇都具有很高的稳定性并且它们的结构和成键性质都和体材料Fe_2O_3有很大的不同;NO主要以N端吸附在Fe_2O_3团簇Fe-top位。NO在(Fe_2O_3)_n团簇上吸附为化学吸附,对应于n从2~6,吸附能分别为1.792、1.976、2.799、2.963和2.536 eV。Mulliken布局分析结合NO吸附前后的态密度分析表明:吸附前后电子由NO向(Fe_2O_3)_n团簇转移,吸附时NO的5口轨道趋向于转移电子给Fd^(3+)的d轨道,使Fe位形成d^(10)稳定电子构型,同时Fe反馈电子给NO的知反键轨道,总体上为NO失去电子。

The properties of （Fe2O3）.（2≤n≤6） clusters and adsorption of NO molecule on them have been studied by the Perdew-Burke-Ernzerh （PBE） generalized gradient approximation（GGA） and the double-number polarization functions of DNP with the Dmol3 program in Materials Studio package based on the density functional theory （DFT）. The optimized results indicated that the Fe-O bond of all the clusters was shorter than the bulk material while the binding energy of all the ground state of clusters was larger than the average energy of Fe2O3. So the structures and bonding properties of the clusters are different from the bulk Fe2O3. The frontier molecular orbitals and Fulcui function analysis indicated that the best adsorption sites of （Fe2O3）, clusters are Fe sites. NO adsorpted with N-down on the Fe-（Fe2O3）, sites are chemisorption and resulted in favorable structures with adsorption energies of 1.792, 1.976, 2.799, 2.963 and 2.536 eV, respectively. An analysis of the density of states, charge population before and after the adsorption showed that electrons transferred from NO to the surface of the （Fe2O3）,（2≤n≤6） clusters and that the N-O bond was elongated. The interaction between the adsorbed molecule and the substrate mainly arises from the 2π anti-bonding orbital of NO and the d orbital of Fe atom. NO lose electrons under the joint action of 2π antibonding orbitals get electrons and its 5σ orbitals lose electrons.