Li Feng, Aeberhard Urs, Wu Hong, Qiao Man, Li Yafei
School of Science, Nanjing University of Posts and Telecommunications Nanjing Jiangsu 210023 China.
IEK-5 Photovoltaik, Forschungszentrum Jülich 52425 Jülich Germany.
RSC Adv. 2018 May 25;8(35):19432-19436. doi: 10.1039/c8ra02492h.
As one of the most prominent metal-hydrides, beryllium hydride has received much attention over the past several decades, since 1978, and is considered as an important hydrogen storage material. By reducing the dimensionality from 3 to 2, the beryllium hydride monolayer is isoelectronic with graphene; thus the existence of its two-dimensional (2D) form is theoretically feasible and experimentally expected. However, little is known about its 2D form. In this work, by a global minimum search with the particle swarm optimization method density functional theory computations, we predicted two new stable structures for the beryllium hydride sheets, named α-BeH and β-BeH monolayers. Both structures have more favorable thermodynamic stability than the recently reported planar square form (, 2017, , 8740), due to the forming of multicenter delocalized Be-H bonds. Utilizing the recently developed SSAdNDP method, we revealed that three-center-two-electron (3c-2e) delocalized Be-H bonds are formed in the α-BeH monolayer, while for the β-BeH monolayer, novel four-center-two-electron (4c-2e) delocalized bonds are observed in the 2D system for the first time. These unique multicenter chemical bonds endow both α- and β-BeH with high structural stabilities, which are further confirmed by the absence of imaginary modes in their phonon spectra, the favorable formation energies comparable to bulk and cluster beryllium hydride, and the high mechanical strength. These results indicate the potential for experimental synthesis. Furthermore, both α- and β-BeH are wide-bandgap semiconductors, in which the α-BeH has unusual mechanical properties with a negative Poisson's ratio of -0.19. If synthesized, it would attract interest both in experiment and theory, and be a new member of the 2D family isoelectronic with graphene.
作为最突出的金属氢化物之一，氢化铍自1978年以来在过去几十年中受到了广泛关注，并被视为一种重要的储氢材料。通过将维度从三维降低到二维，氢化铍单层与石墨烯等电子；因此其二维形式的存在在理论上是可行的，并且在实验中也有所预期。然而，人们对其二维形式知之甚少。在这项工作中，通过使用粒子群优化方法进行全局最小搜索和密度泛函理论计算，我们预测了氢化铍片材的两种新的稳定结构，分别命名为α-BeH和β-BeH单层。由于形成了多中心离域的Be-H键，这两种结构都比最近报道的平面正方形形式（, 2017,, 8740）具有更有利的热力学稳定性。利用最近开发的SSAdNDP方法，我们发现α-BeH单层中形成了三中心两电子（3c-2e）离域的Be-H键，而对于β-BeH单层，首次在二维体系中观察到了新型的四中心两电子（4c-2e）离域键。这些独特的多中心化学键赋予了α-和β-BeH高结构稳定性，这通过它们声子谱中没有虚模、与块状和团簇氢化铍相当的有利形成能以及高机械强度得到了进一步证实。这些结果表明了实验合成的潜力。此外，α-和β-BeH都是宽带隙半导体，其中α-BeH具有不寻常的力学性能，泊松比为-0.19。如果合成成功，它将在实验和理论上都引起关注，并成为与石墨烯等电子的二维家族的新成员。
