Predicting mechanical and thermal properties of 2D materials using Molecular dynamics and ab initio simulations based on Density Functional Theory

The exploration of two-dimensional (2D) materials, including graphene, hexagonal boron nitride (h-BN), and borophene, has become a pivotal domain within materials science due to their extraordinary mechanical and electrical properties. This dissertation presents a comprehensive suite of molecular dynamics (MD) simulations, reactive molecular dynamics (RMD) and Density Functional Theory (DFT) calculations aimed at deciphering the multifaceted behaviors of these nanomaterials, focusing particularly on their mechanical and thermal responses under various conditions, which are crucial for real-world applications. The body of work detailed in this thesis scrutinizes the mechanical properties of single-layer h-BN nanosheets, revealing the influences of temperature, topological defects, and strain rates on their tensile strength and elasticity. By simulating a spectrum of grain boundary misorientations and defects across different temperatures, this research elucidates the dependence of mechanical strength on the misorientation angles of grain boundaries, highlighting a unique mechanical response in high-angle misorientation grain boundaries under uniaxial tension. Additionally, the temperature sensitivity of these properties is rigorously analyzed, with findings indicating a significant de-crease in fracture strength and strain-at-failure with increased temperatures, notably in low-angle grain boundaries. Furthermore, this dissertation delves into the realm of fracture mechanics, examining centered-crack and notch effects in both pristine and polycrystalline nanosheets. The impact of initial crack sizes on crack propagation under mixed-mode loading conditions is meticulously studied, revealing the tendency for crack bifurcation in polycrystalline borophene sheets, a phenomenon independent of initial crack size and strain rates. These insights are paramount for ad-vancing our understanding of material failure processes, especially for applications requiring robust mechanical performance. The thesis also ventures into the innovative field of nanopore sequencing technology, where the precision fabrication of nanopores within polycrystalline boron-nitride nanosheets is investigated through ion bombardment MD simulations. The study examines the effects of cluster size, kinetic energy, and bombardment location on nanopore formation, providing critical parameters for optimizing nanopore quality and size—factors essential for the advance- ment of genomic sequencing technologies. Reactive molecular dynam- ics simulations further shed light on the mechanical and thermal behav- ior of borophene nanofilms. The research presents a detailed analysis of mode I fracture behavior in polycrystalline borophene, studying crack propagation under various loading conditions and the influence of grain boundary misorientation on crack paths. Equilibrium molecular dynam- ics (EMD) simulations are employed to predict the thermal conductivity of pristine borophene, offering valuable data for its potential application in thermal management systems. In conclusion, this thesis contributes significant new knowledge to the field of nanomaterials engineering, pro- viding a detailed examination of the mechanical and thermal properties of 2D materials. The findings not only enhance the theoretical under- standing of these materials but also offer practical for their integration into advanced technologies. The multifaceted investigations carried out in this dissertation underscore the delicate balance between atomic-scale features and macroscopic material properties, revealing how intrinsic and extrinsic factors such as defects, grain boundaries, and environmental con- ditions play a defining role in the performance of 2D materials. The com- prehensive computational approach adopted here—spanning MD, RMD, and DFT simulations—has enabled a series of novel findings. Notably, it has been demonstrated that the mechanical strength of polycrystalline h-BN is robust across a range of grain boundary configurations and that this strength is maintained even at elevated temperatures, suggesting that grain boundaries may not significantly impair the material’s mechanical integrity in practical applications. The work also provides groundbreak- ing insights into the optimal conditions for nanopore creation within poly- crystalline boron-nitride, thereby paving the way for more precise and ef- ficient DNA sequencing devices. In addition, the dissertation presents a thorough examination of the fracture mechanics in borophene, a material with a bright future in nanoelectronics and energy applications due to its exceptional properties. The observations of crack propagation behavior under mixed-mode loading provide a deeper understanding of the mate- rial’s fracture dynamics, critical for designing borophene-based devices that can withstand mechanical stresses. The thermal conductivity analy- sis of borophene opens doors for its application in areas where superior thermal management is required. The outcomes of this research not only advance the fundamental science behind 2D materials but also hold the potential to significantly impact several key technological areas. By opti- mizing the mechanical and thermal properties of these materials, this work contributes to the development of the next generation of electronics, en- ergy storage systems, and nanotechnology-based medical devices. This dissertation stands as a testament to the power of computational simula- tions in materials science, offering predictive insights that guide experi- mental work and drive innovation. The depth and breadth of the research presented herein not only fill existing knowledge gaps but also create a springboard for future studies aimed at harnessing the full potential of 2D materials. It is anticipated that the methodologies and findings detailed in this comprehensive study will serve as a valuable resource for scientists and engineers seeking to explore and exploit the remarkable properties of graphene, h-BN, borophene, and beyond.