Atomic scale electro-mechanics of two dimensional materials using modeling and simulations

Abstract

Objective molecular dynamics (OMD) is a generalization of the universally adopted periodic boundary conditions (PBCs) used in atomic simulations. By taking advantage of the translational symmetry, molecular dynamics under PBCs reduces the overall number of atoms that need to be simulated in crystalline bulk materials. Unfortunately, PBCs are not generally applicable to structures having helical and rotational symmetries. OMD replaces the use of translational symmetry with helical and rotational symmetries, which are widely present in a number of nanostructures and nano materials. Such structures include carbon nanotubes, mechanically deformed nanomaterials such as 2D films subjected to bending and torsion. The recent capability resulted from the coupling of self-consistent charge density functional tight binding (SCC-DFTB) with OMD enables unprecedented calculations on helical and mechanically deformed two-dimensional materials with quantum mechanical accuracy. This coupling is especially important for simulating materials with complex bonding such as zinc oxide thin films, which contains charged species. It also captures the charge redistribution under mechanical deformation in layer bending. In this thesis, we use this capability to simulate bending of 2D materials and build continuum elastic models based on the atomistic data. These structures of interest include phosphorene, boron nitride and zinc oxide. Mechanical properties of 2D materials are studied mainly via bending deformations. Bending deformations lead to charge distribution across the thickness in two-dimensional materials. This effect can produce structural effects in nano-films. Zinc oxide layers are important because of their properties of piezo-electric effects with potential applications as important energy materials. In addition, we also study bending and in-plain deformation of boron nitride. This understanding of bending deformations will help advance the development of strain engineering technology for these 2D materials.