外吸附CO过渡金属团簇Pd_5(CO)_n(n=1～6)的几何结构、电子性质、前线轨道和磁性的密度泛函计算研究

Density functional study on structural,electronic,frontial orbital,and magnetic properties of the transitional metal clusters Pd_5(CO)_n(n = 1-6)

本文采用密度泛函理论中的广义梯度近似对过渡金属团簇Pd_5(CO)_n(n=1～6)的几何结构、电子性质、前线轨道和磁性进行计算研究,由结构优化可知:当CO分子的C原子吸附在面桥位时形成的单重态Pd_5CO结构热力学最稳定,和Zanti等人(Eur.J.Inorg.Chem.2009,3904)得到的结论一致.Pd_5(CO)_2和Pd_5(CO)_3最稳定结构中,第二个和第三个CO分子都吸附在边桥位,而第一个CO分子吸附在面桥位.但是对于最稳定的Pd_5(CO)_n(n=4,5,6),所有的CO分子都位于边桥位.从吸附能的角度看,Pd_5(CO)_2应该是最容易得到的吸附产物.由能隙可知:Pd_5(CO)_n(n=1～6)的动力学稳定性相比较Pd_5有所增加,但是并不会随着CO分子数目的增加而呈现递增或者递减的规律.其中Pd_5(CO)_3具有最好的动力学稳定性.CO在Pd_5上发生非解离性化学吸附,CO健的强度变化逐渐变小.CO对HOMO和LUMO贡献很小,使得HOMO和LOMO的成分发生一定的改变.由VIP和VEA计算可知:随着CO数目的增加,Pd_5(CO)_n(n=1～6)的失电子能力逐渐降低,而得电子能力逐渐增强.Pd_5具有2_(μB)的磁矩,但是Pd_5(CO)_n(n=1～6)的磁性完全淬灭.

The generalized gradient approximation based on density functional theory is used to analyze the structural, electronic, frontial orbital and magnetic properties of the transition metal clusters Pd5（CO）n（n=1 to 6）. For Pd5CO, the singlet state structure with C atom adsorbed on the hollow site of three Pd atoms in the form of CO molecule is the most stable, as same as the conclusion reported by Zanti et al （Eur. J. Inorg. Chem. 2009, 3904）. For Pd5（CO）2 and Pd5（CO）3, the second and third CO molecules are adsorbed on the bridge sites and the first CO molecule is adsorbed on the threefold hollow sites. But for the most stable Pd5（CO）n（n=4,5,6）, all CO molecules are adsorbed on the bridge sites. The adsorption energy analysis shows that Pd5（CO）2 should be the most possible adsorption product. It can be known from the Eg that Pd5（CO）n（n=1 to 6） have enhanced dynamical stability compared to Pd5, but do not display the increasing or decreasing rule with the increase of the CO moleculars. Amongest, Pd5（CO）3 has the best dynamical stability. Chemisorption of CO onto the Pd5 cluster surface is a non-dissociative adsorption process and the strength of C-O bond became weaker with the increasement of CO molecules. CO have a little component of HOMO and LUMO, but the adsorption of CO cause the edistribution of the compoment of HOMO and LOMO. It can be explored from VIP and VEA that, along with the increase of the CO molecules, the ability of detaching electrons is weakened and the ability of obtaining electrons is improved. The Mulliken charge analysis shows that the magnetic moment of Pd5 is 2μB, however, Pd5（CO）n（n=1 to 6） has no magnetic moment.