There are many simulation studies of mechanical properties of graphene nanoribbons (GNR), but there is a lack of agreement regarding elastic and plastic behavior. In this paper we aim to analyze mechanical properties of finite-size GNR, including elastic modulus and fracture, as a function of ribbon size. We present classical molecular dynamics (MD) simulations for three different empirical potentials which are often used for graphene simulations: AIREBO, REBO-scr and REAXFF. Ribbons with and without H-passivation at the borders are considered, and the effects of strain rate and different boundaries are also explored. We focus on zig-zag GNR, but also include some armchair GNR examples. Results are strongly dependent on the empirical potential employed. Elastic modulus under uniaxial tension can depend on ribbon size, unlike predictions from continuum-scale models and from some atomistic simulations, and fracture strain and progress vary significantly amongst the simulated potentials. Because of that, we have also carried out quasi-static ab-initio simulations for a selected size, and find that the fracture process is not sudden, instead the wave function changes from Bloch states to a strong interaction between localized waves, which decreases continuously with distance. All potentials show good agreement with DFT in the linear elastic regime, but only the REBO-scr potential shows reasonable agreement with DFT both in the non-linear elastic and fracture regimes. This would allow more reliable simulations of GNRs and GNR-based nanostructures, to help interpreting experimental results and for future technological applications.

中文翻译：

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有限尺寸石墨烯纳米带的模拟机械性能

石墨烯纳米带 (GNR) 的机械性能有许多模拟研究，但在弹性和塑性行为方面缺乏一致意见。在本文中，我们旨在分析有限尺寸 GNR 的机械性能，包括弹性模量和断裂，作为带材尺寸的函数。我们提出了三种不同经验势的经典分子动力学 (MD) 模拟，这些经验势通常用于石墨烯模拟：AIREBO、REBO-scr 和 REAXFF。考虑了在边界处有和没有 H 钝化的带，并探讨了应变率和不同边界的影响。我们专注于 zig-zag GNR，但也包括一些扶手椅式 GNR 示例。结果在很大程度上取决于所采用的经验潜力。单轴拉伸下的弹性模量取决于带材尺寸，与来自连续尺度模型和一些原子模拟的预测不同，断裂应变和进展在模拟势之间存在显着差异。正因为如此，我们还对选定的尺寸进行了准静态从头算模拟，发现断裂过程并不是突然的，而是波函数从布洛赫态转变为局域波之间的强相互作用，不断减小与距离。在线性弹性状态下，所有电位都与 DFT 有很好的一致性，但在非线性弹性和断裂状态下，只有 REBO-scr 电位与 DFT 显示出合理的一致性。这将允许对 GNR 和基于 GNR 的纳米结构进行更可靠的模拟，以帮助解释实验结果和未来的技术应用。