Density Functional Theory Studies On The Structures And Properties Of Au₂X_n(X=F,H,OF And 1?n?10) Clusters

Based on density functional theory,the Au₂X_n(X=F,H,OF;1?n?10)cluster systems are systematically studied by using Gaussian 09 software,and the relatively stable structures are obtained through global optimization.Meanwhile,the physical and chemical properties for the lowest isomers of these clusters,such as stability,magnetism,and spectroscopies are also studied.In the calculations for all clusters,the Lan L2DZ pseudopotential basis set is adopted for Au atoms.With the PW91PW91functional,the 6-311+g(d)and 6-311++g(d,p)basis sets are applied for the F atoms in Au₂F_n and the O and F atoms in Au₂(OF)_n,respectively.For the H atoms in Au₂H_n,the6-311++g(d,p)basis set is adopted with the B3LYP functional.The analysis on the geometric structures and stabilities of these clusters shows that with the increase of the size of the clusters the structures of the lowest isomers of the clusters change from the simple planar configuration to the complex 3D one,and the growth patterns can be generally described as the gold atoms connecting with multiple fluorine atoms,hydrogen molecules and oxygen fluorine atoms,respectively.From n=5,Au₂H_n mainly manifests the physical adsorption of hydrogen molecules.The average binding energy analysis shows that Au₂F₆ has the highest thermodynamic stability in the systems.Au₂H_n(1?n?4)clusters have the larger energy gap values than Au₂X_n(X=F,OF;1?n?10)clusters and show the higher chemical stabilities.Au₂H₄exhibits the highest chemical stability,while Au₂(OF)₂ shows good chemical activity.The VIP and VEA values of Au₂X_n(X=F,OF;1?n?10)clusters are always higher than those of Au₂H_n(1?n?4)clusters.As regards the electronic structures of these clusters,the magnetic moments of the clusters range from 0 to 3?_B,whereas the total magnetic moments of Au₂F₂,Au₂F₄,Au₂H₂ and Au₂(OF)₂ are zero.The non-zero total magnetic moments of the other Au₂F_n(1?n?10)and Au₂H_n(n=1-4)clusters come mainly from the local magnetic moments of Au atoms,while the total magnetic moments of the other Au₂(OF)_n(1?n?10)clusters are mainly ascribed to the local magnetic moments of O atoms,associated with both anti-ferromagnetic and ferromagnetic coupling between the atoms.For the dipole moments of the clusters,the total dipole moments of Au₂F₆ and Au₂F₁₀ are zero,belonging to non-polar molecules,while Au₂F₄ has the largest dipole moment.The cluster polarizability tensor is mainly distributed along the XX,YY and ZZ axes.The largest average polarizability tensor<a>for Au₂(OF)₁₀ exhibits the strongest nonlinear optical effect,resulting in the most feasibility for this system to be polarized.With the largest average value<a>of Au₂H_n,it displays the strongest delocalization effect and the relatively unstable electronic structure.Au₂(OF)₁₀ has the strongest response ability of the system due to its largest?a.The density of states(DOS)curves of the clusters are mainly distributed between-0.6?0.2 a.u..With the increase in size,the molecular orbital also changes from a single Au atomic orbital to a complex hybrid orbital.Au₂F₂,Au₂(OF)and Au₂H₃ clusters show the strongest covalent bondings in their respective cluster systems and hence higher chemical stabilities.As for the spectroscopic analysis,there are many vibration peaks in the infrared and Raman spectra of the clusters,mainly locating in the range of 0-4500 cm^-1.The highest peaks mainly originate from the stretching vibration between X atoms or that between X and other atoms.The strongest peaks of Au₂H_n(n=1-4)clusters are obviously higher than those of Au₂X_n(X=F,OF;1?n?10)clusters with the same n.The UV-Vis spectra of these clusters are largely in the range of 100-3000 nm,among which Au₂F_n(n=3,7-10)and Au₂(OF)_n(n=2,4,7,8)show strong absorption peaks in the visible region,indicating that these clusters are likely to be the potential new type catalytic nanomaterials under visible light.