Negative Poisson’s ratio (NPR) in auxetic materials is of great interest due to the typically enhanced mechanical properties, which enables plenty of novel applications. In this paper, by employing first-principles calculations, we report the emergence of NPR in a class of two-dimensional honeycomb structures (graphene, silicene, h-BN, h-GaN, h-SiC, and h-BAs), which are distinct from all other known auxetic materials. They share the same mechanism for the emerged NPR despite the different chemical composition, which lies in the increased bond angle (θ). However, the increase of θ is quite intriguing and anomalous, which cannot be explained in the traditional point of view of the geometry structure and mechanical response, for example, in the framework of classical molecular dynamics simulations based on empirical potential. We attribute the counterintuitive increase of θ and the emerged NPR fundamentally to the strain-modulated electronic orbital coupling and hybridization. It is proposed that the NPR phenomenon can also emerge in other nanostructures or nanomaterials with similar honeycomb structure. The physical origin as revealed in our study deepens the understanding on the NPR and would shed light on future design of modern nanoscale electromechanical devices with special functions based on auxetic nanomaterials and nanostructures.

由于通常具有增强的机械性能，因而引起了许多新颖的应用，因此，在声学材料中负泊松比（NPR）引起了人们的极大兴趣。在本文中，通过采用第一性原理计算，我们报告了NPR在一类二维蜂窝结构（石墨烯，硅烯，h -BN，h -GaN，h -SiC和h -BAs）中的出现。与所有其他已知的助燃材料不同。尽管化学成分不同，但它们对于出现的NPR具有相同的机理，这在于键角（θ）增大。但是，θ的增加这是非常有趣和反常的，无法用传统的几何结构和机械响应的观点来解释，例如，在基于经验潜能的经典分子动力学模拟的框架中无法解释。我们将θ的反直觉增加和出现的NPR从根本上归因于应变调制的电子轨道耦合和杂交。有人提出，NPR现象也可能出现在其他类似蜂窝结构的纳米结构或纳米材料中。在我们的研究中揭示的物理起源加深了对NPR的理解，并将为未来基于具有膨胀功能的纳米材料和纳米结构的具有特殊功能的现代纳米级机电设备的设计提供启发。