First Principle Study Of (MgO)_n, (BeO)_n And Ge₆Li₆ Clusters

Recently,nano-materials have been widely studied,because of its valuable role in scientific research and special characters.Cluster is one of the most important nano-materials,so the study of cluster is vital to scientific research.Based on density functional theory,structure,electronic,spectral and aromatic properties of(MgO)_n, (BeO)_n(n=2-10) and Ge₆Li₆ clusters have been studied in this paper.The work focus on three parts:1.First Principle Study of Ge₆Li₆ Clusters.Possible structures of Ge₆Li₆ cluster have been investigated with density functional theory(DFT) in this part.It is found that all the planar-like Ge₆Li₆(six germanium atoms in one plane) are aromatic,except the structure with C₂ symmetry. The ground state Ge₆Li₆ is D_2h symmetry.According to the analysis of NICS,the planar ground state structure of Ge₆Li₆ with D_2h symmetry has similar aromaticity with benzene and almost the same aromaticity to the ground state Si₆Li₆.Molecular orbital analysis shows that there exist delocalized electrons or delocalizedÏ€molecular orbital,which well demonstrates dramatic NICS(1) value of the ground state Ge₆Li₆. In addition,to facilitate later comparison to experiment results and further research, some spectral properties(infrared,Rama and absorption spectrum) and a possible synthesis route based on high exothermicity and the conversation of molecular orbital symmetry are also studied.2.A Simple Theoretical Model for Ring and Nanotube Radial Breathing Mode.The radial breathing modes(RBMs) of(MgO)_n and(BeO)_n nanorings(n=3-10) are calculated using the density functional theory.The linear dependence of RBM frequency on the inverse diameter is found for larger diameter rings,while the variation of bond length may cause deviations from the linear behavior.If the ring diameter is small enough that higher terms cannot be neglected,the deviations may become dramatic,which are caused by the variation of bond length and the inverse cubic correction.From the point of chemical bond view,using one-dimensional harmonic oscillator of the radial breathing vibration and the method of cascade and parallel connection of "springs",a simple theoretical model is obtained and well explain the above linear behaviors and deviations.The model can also be extended to nanotubes and well demonstrate the relationship between radial breathing frequencies of carbon nanotubes(CNTs) and nanotube diameters.3.Structure,Electronic and Aromatic Properties of(MgO)_n and(BeO)_n(n=2-9) Nanorings.Based on density functional theory,structure and properties such as energy, molecular orbital and aromaticity of(MgO)_n and(BeO)_n(n=2-9) clusters have been studied in this part.It is found that the highest occupied molecular orbital exhibits even-odd oscillation caused by different symmetry of molecules.NICS analysis shows that molecules are aromatic for n=2 clusters and are nonaromatic for n≥3 clusters.