Study On The Mechanical And Dielectric Properties Of Low-dimensional Nanomaterials With Multiscale Simulations

In this thesis, the mechanical and dielectric properties of low-dimensional nanomaterials have been studied by continuum-elasticity theory, first-principle calculation and molecular mechanics. As examples, zinc oxid (ZnO) and copper have been studied from four different aspects:surface effect, doping effect, size effect, and nonlinear effect under large strain.The scale range and efficiency of these calculation and simulation methods have been discussed and improved. A theoretical calculation and simulation of low-dimensional materials have been achieved.The elastic and static dielectric constants of pure and dopped ZnO have been studied by first-principles calculations. It was observed that the elastic constants show an increase with In doping and a decrease with Mn doping. For the case of the static dielectric constant, shows a gradual decrease with Mn doping.The size dependent Young’s moduli and static dielectric cosntant of ZnO nanowires have been studied by molecular mechanics methods. The strain and size dependent Young’s moduli were obtained for [0001] oriented ZnO nanowires with diameter ranged from1.8nm to6.0nm. The constant term of Young’s moduli of ZnO NWs is smaller than those of the bulk, and it decreases from121.5to96.7GPa as the diameter decreases. The linear term increases rapidly as the diameter decreases and changed from negative to positive when the diameter is3.6nm. The linear term was124.4GPa when diameter is6.0nm, and it reached248.8GPa when the diameter is1.8nm.An accurate and efficient method has been reported for calculating the nonlinear elastic response of thin, homogeneous films to biaxial strain in arbitrary planes using a continuum-elasticity theory model. The general analytic expressions were derived for the elastic energy and the Poissons ratio under biaxial strain for cubic crystals. The biaxial Poisson’s ratio showed a linear relationship with strain when high-order elastic constants are considered. The expressions were verified with simulated biaxial Poisson’s ratio and elastic energy of copper by density-functional theory calculations for three high symmetry planes.