Density Functional Theory Studies On The Structures And Properties Of MX_n(M=Au,Pt;X=Se,Te;2≤n≤5) Clusters

Based on the B3PW91 functional and the LANL2DZ pseudopotential,the geometrical structures of MX_n（M=Au,Pt;X=Se,Te;2≤n≤5）clusters are optimized,and a series of stable structures are obtained.For these clusters,the relevant physical and chemical properties are further studied and analyzed.For the geometry of the clusters,the structure of the lowest isomer changes from the simple straight-linear and planar configurations to the complex planar and three-dimensional ones with the increase of the number n of X atom.The interactions of<M-Te>and<Te-Te>bonds are slightly weaker than the corresponding<M-Se>and<Se-Se>bonds,respectively,and AuX₅ and PtX₄ have the highest thermodynamic stability among the clusters.Further,AuSe₃ and PtTe₂ clusters have the strongest ability to attract the bonding electrons among the systems.And AuTe₄ has the smallest energy gap and hence the highest chemical activity,while AuSe₃ and PtSe₄ have the highest chemical stability.The hybridization of the Se clusters is stronger than the Te clusters.As for the electronic structures,selenium and tellurium clusters have similar curves of total density of state,mainly because of both elements in the same main group of the periodic table of elements and hence of similar chemical properties.AuX₅ shows higher chemical stability and the covalency.The<M-Se>bond length is shorter than the corresponding<M-Te>one,and the distances between the peaks on the left and right sides of Fermi energy level of the selenium clusters are slightly larger than the tellurium ones.Most of the polarizability tensors lie in the principal axial directions of XX,YY and ZZ.The maximum of the average value of the polarizability tensors of a single atom<?>is 44.40 a.u.for AuTe₅ cluster,associated with the unstable electronic structure and the obvious delocalization effect.MX₅ has the strongest bonding interactions and nonlinear optical effect of the systems.And the distributions of the magnetic moments depend strongly upon the symmetries of the clusters.As regards the spectral properties of the clusters,the peaks of infrared（IR）spectra locate mainly in the range of 0-350 cm^-1.The vibration modes corresponding to the highest peaks are mainly the stretching vibration of M or X atoms.The peaks in Raman spectra of these clusters locate mainly in the range of 50-350 cm^-1.Most of the vibration modes corresponding to the highest peaks belong to the stretching vibration of M or X atoms.There are a few vibrational peaks in the UV-Vis spectra.AuTe₂ and AuSe₃ as well as MX₅ display obvious absorption peaks in the visible region（200-800 nm）,indicating that these clusters may have good visible light activity and potential visible light catalytic properties.PES spectra show few peaks,and the electronic energy corresponding to the highest peak increases with the increase of atomic numbers.For the adsorption properties of the clusters,the<Au-Te>and<Te-Te>bond lengths of AuTe₄H₂O cluster are longer and shorter than the unadsorbed cluster,indicating that the<Au-Te>and the<Te-Te>bonds are weakened and enhanced,respectively,when a water molecule is adsorbed.Further,the<Au-Te>and<Te-Te>bonds of AuTe₄O₂cluster are even longer and shorter,suggesting that the<Au-Te>and the<Te-Te>bond interactions are further weakened and enhanced,respectively,for the adsorption of an oxygen molecule.Both AuTe₄H₂O and AuTe₄O₂ clusters are chemisorption.The ability of AuTe₄ cluster to adsorb oxygen is stronger than water,and it may be used as the potential oxygen adsorption materials.