First-principle Study On The Structure And Properties Of The Pt-alloy Clusters And Monolayer Anatase TiO₂（001） Nanosheet

Bimetallic clusters, composed of two different metal elements, are of greater interestthan monometallic ones for the improvement of catalytic properties of metal particles. Thegreat advantage of bimetallic clusters or nanoalloys is that their properties may be tuned byvarying not only their size and geometries, but also their composition. Recently, platinumalloyed with some3d transition metal nanoparticles have been aroused considerableinterests by chemists and physicists due to their unique physical and chemical properties,particularly, their superior catalytic activities for a number of reactions. In this paper,Gaussian03and Dmol3programs based on density functional theory are applied to optimizethe geometric structures of PtnNim(n+m=7, n, m≠0) and TM@Pt6(TM=Sc, Ti, V, Cr, Mn,Fe, Co, Ni, Cu and Zn) clusters, respectively, their structural stability, electronic structureand magnetic properties, including many other physical and chemical properties, areinvestigated. At the same time, we also pay attention to the abnormal properties of twodimension nanomaterials such as grapheme, with the current experimental research on theTiO2semiconductor, we have investigated the structural, electronic and magnetic propertiesof anatase TiO2(001) nanosheets. The research contents and results are as follows.(1) All the ground state structures of PtnNimclusters are cube structure, symmetry arelower and multiplet are higher. Pt5Ni2is the most stable one of PtnNim（n+m=7, n, m≠0）clusters. From magnetic analysis, the total magnetic moment of Pt2Ni5cluster is the largest,while the Pt5Ni2cluster is the smallest. Local magnetic moment belonging to the atom at thesymmetrical position are equal, and Ni atom plays a leading role in magnetism of the binaryPtnNim(n+m=7, n, m≠0) clusters.(2) The calculation for the energy level, HOMO-LUMO gap, natural bond orbital, theinfrared and Raman spectrum and the aromatic properties of the PtnNim(n+m=7, n, m≠0)clusters indicate that the Fermi level are determined by the number of Pt atom and only justthe Pt1Ni6and Pt6Ni1have direct energy gap; Multifarious orbital hybridization are found inthe frontier molecular orbital and the rich platinum or nickel cluster have smaller energy gapthan others; The mainly direction of charge transfer is from Ni atom to Pt atom, which bringabout strong orbital hybrid phenomenon and high chemical activity in PtnNim(n+m=7)clusters; There are many obvious peak in all the IR and Raman spectrum, the strongest peakposition of IR spectrum are locate at above150cm-1, that of Raman spectrum are above200cm-1. The frequency position of the strongest peak in both IR and Raman spectrum ofPtnNim(n+m=7) clusters are clear and obvious; All the PtnNim(n+m=7) cluster have aromaticity, moreover some cluster in certain special position have antiaromaticity ornonaromaticity, the aromaticity are directly bound up with its geometric structure.(3) The calculated results for the structural, electronic, and magnetic properties of3dtransition-metal impurity doped Pt6clusters show that all the ground states of the TM@Pt6clusters are cubic structure and have similar structure which can be defined as some-cappedquadrangular pyramid. We found that there is two chiral structures in all the stable structureof the TM@Pt6clusters, of which the structure are completely mirror symmetry. Most of thedoped structures show larger binding energy than pure Pt7cluster, indicating doping the3dtransition metal atoms could stabilize the pure platinum cluster. The HOMO-LUMO gapsresults show that most of the doped clusters have more chemical activity than pure Pt7cluster. The magnetism calculations demonstrate that variation range of the magneticmoments of TM@Pt6clusters is from0to7μB, indicating that TM@Pt6clusters could hasthe potential utility in designing new spintronic nanomaterials with tunable magneticproperties.(4) The calculation for the electronic structure and magnetic properties of the monolayeranatase TiO2(001) nanosheet suggest that there are obvious difference between the monola-yer anatase TiO2(001) nanosheet and its bulk phase, Most Specifically the difference attrib-ute to the bond length and bond angle among the Ti and O atoms. In contrast to its bulk pha-se the band gap of monolayer anatase TiO2(001) nanosheet is indirect and is increasing to3.23eV. The structural changes of defective monolayer anatase TiO2(001) nanosheets afterDFT calculation is concentrated on the vicinity of defect. For the vacancy defect VTiand VO,the former is better than the latter on the reducing band gap value and the two nanosheet areferromagnetic. The whole defective nanosheets can reduce the band gap value as to the sub-stituted nanosheets. Excluding the S atom the substituded nanosheet are ferromagnetic andthe nanosheet substituded by C atom have the biggest magnetic moment.