The Investigation Of Structures And Properties Of Pt_nNi_55-n?n=0?55? Nanoclusters And The Adsorption Of Methanol Using Density Functional Theory

The composition-dependent icosahedral (ICO) structures of PtnNi55-n bimetallic nanoclusters are explored to investigate the structural, electronic and magnetic properties and the adsorption of methanol using density functional theory. The main conclusions are given as follows:1. For PtnNi55-n nanocluster, Pt preferentially segregates to the surface and Ni prefers being in the core. With the increase of Pt atoms, the excess energy decreases at first then it increases, when Pt/Ni?1:1(Pt28Ni27) the structure has the lowest excess energy among the study system. It is noticed that the structures with the greater number of Pt-Ni bonds are more energetically stable on account of the fact that the interaction of Pt-Ni bond is stronger than that of Ni-Ni and Pt-Pt bonds. In addition, the density of states of d-band for Ni and Pt in PtnNi55-n NPs reveals that the Ni-3d and Pt-5d orbitals paly the dominant role in electronic states. Ni d-band has a more remarkable effect on Pt d-band than that of Pt d-band on Ni d-band. Furthermore, the PtnNi55-n NPs present remarkable magnetic behavior and the total magnetic moments increase with Ni atoms increasing. The magnetic moment of Pt54Ni1 NP is larger than that of Pt55 when one Ni atom occupies center, while when the Ni atom occupies surface sites, the magnetic moment of Pt54Ni1 is much lower than that of Pt55. For Pt1Ni54 NP, the magnetism is enhanced comparing with Ni55 when one Pt atom occupies edge site.2. Compared with the free methanol, the C-O and O-H bonds in all adsorption structures are stretched, which indicates that the C-O and O-H bonds are activated. For the structure at every Pt/Ni ratio, the C-O bond in T1 site and O-H bond in B1 site are longer than other sites at the same Pt/Ni ratio, and the C-O and O-H bonds in Pt28Ni27 nanocluster are longest in all structures. The oxygen atom in methanol reacts with metal aroms through its lone-pair electron during the adsorption process, which leads to the charge transfer from metal atoms to methanol. The order of the amount of barder charge is T1>T2>B2>B1 at every Pt/Ni ratio except for Pt55 and Ni55 nanoclusters.The amount of barder chger are largest on T1,T2 and B1 sites for Pt28Ni27, Pt14Ni41 and Pt44Ni11 nanoclusters, respectively. By comparing the density of states (DOS) of adsorbed clusters with free methanol and PtnNi55-n nanoclusters, it is noticed that the DOS peaks in all structures move to lower energy. There forms ? bonds between p-ortibal of oxygen atom and d-orbital of Pt or Ni atoms, which results in the strong adsorption. The results of vibrational frequency illustrate that the O-H, O-C and C-H bonds present red shift after adsorption and the vibrational modes inclue stretching vibration and flexural vibration.