Effect Of The Doping On Properties Of PtNi Bimetallic Clusters And PtNi Clusters Adsorbed By Single-Walled Carbon Nanotubes:a First-Principles Study

The structural, electronic, and magnetic properties of PtNi bimetallic clusters with different Pt/Ni ratios are investigated by a first-principles method. The properties of PtNi clusters vary with the replacement of Pt atoms of Ni atoms. In this thesis, the main results are listed as follows.1. First-principles method based on the density functional theory has been utilized to calculate the structural, electronic and magnetic properties of Pt13-nNin (n=0-13) clusters. For Pt13-nNin clusters, Ni atoms are mainly found in the cluster core and Pt atoms are segregated to the cluster surface. The calculated binding energies of Pt13-nNin clusters decrease with increasing Ni concentration. Through the bader charge and difference charge density analyses, it is observed that the small charge transfer is from Ni to Pt. In the total and partial density of states of Pt13-nNin clusters, Pt5d and Ni3d orbitals make the main contribution to the electronic states and play an important role in determining the magnetism of Pt13-nNin clusters. From n≥2, the calculated magnetic moments of Pt13-nNin clusters increase to the maximum (8.34μB) in Pt2Ni11cluster as a function of Ni concentration and then decrease slightly. The variation in the magnetic behavior of Pt13-nNin clusters can be attributed to the exchange splitting of the energy bands near the Fermi level.2. The geometrical and electronic properties of PtmNin clusters adsorbed on metallic (9,0) single-walled carbon nanotube support (SWNT) are investigated using density functional theory calculations. The most stable configuations of Pt3-nNin clusters on SWNT are with two atoms (Pt, Ni) binding to SWNT, and the two atoms are both sitting at the bridge sites of skewed C-C bonds. The most stable configuations of Pt4-nNin clusters on SWNT are ones with three atoms in contact directly with the nanotube. For PtmNin cluster on SWNT, Mulliken charge transfer is from SWNT to PtmNin cluster firstly and then changes to be in the opposite direction with the doping of Ni atom, which can be attributed to the loss of electrons from H atoms. With the replacement of Pt atom by Ni atom, the HOMO-LUMO gaps for PtmNin clusters on SWNT are very small. Moreover, SWNT and SWNTs adsorbed on PtmNin clusters show metallic characteristics. For PtNi-SWNT system, the stabilization energy of95.81kJ/mol associated with Ï€Pt127-Nt127â†'σC59-Pt127delocalisation is the strongest by the analysis of natural bond orbital (NBO). Finally, the density of states of PtmNin, clusters adsorbed on nanotubes are analyzed in detail. We find that C-2p, Pt-5d and Ni-3d orbitals make the main contribution near the Fermi level in the partial density of states of Pt2Ni2cluster adsorbed on SWNT, Moreover, there is the strong hybridization between C-2p and Pt-5d orbitals, between C-2p and Ni-3d orbitals, and between Pt-5d and Ni-3d orbitals near the Fermi level.