45 isomers of TinNm(n + m=5=6) clusters=including linear=some planar and some stero configurations=have been predicted by density functional theory method.For five-atom clusters Ti3N2 and Ti2N3=the most stable structures are trigonal bipyramid in D3h symmetry=and for Ti4N cluster=the isomer with one nitrogen atom occupying the center of quasi-tetrahedron is the most stable.In the isomers of Ti4N2 and Ti3N3=the planar networks are more stable=but for Ti2N4=the six-membered ring configuration is the most favorable.Most linear structures can form weak-strong bonds alternately with higher energy.As regards to planar structures=the more Ti-N bonds are formed=the more stable they will be;for stero closed polyhedral isomers=their energies are lower.
A systematic study on geometry,electronic structure and vibrational properties of N-doped TiO2 anatase cluster,within the framework of the density functional theory,has been performed in this work. The calculations confirmed that the most structures in substitutional model consist of a two-coordinate bridge structure and a three-coordinate hollow structure. The calculated results can well explain the red shift in N-doped TiO2 observed in experiments. The study provides an illustration for the N-doped anatase from the viewpoint of chemical bonding theory.
