Two-Dimensional Be₂C with Octacoordinate Carbons and Negative Poisson’s Ratio

Abstract

In this work, we predicted three new two-dimensional (2D) Be 2 C structures, namely, α-Be 2 C, β-Be 2 C, and γ-Be 2 C, on the basis of density functional theory (DFT) computations and the particle-swarm optimization (PSO) method. In α-Be 2 C, a carbon atom binds to eight Be atoms, forming an octacoordinate carbon moiety. This is the first example of an octacoordinate carbon containing material. The other two structures, β-Be 2 C and γ-Be 2 C, are quasi planar hexacoordinate carbon (phC) containing 2D materials. Good stability with these three phases is revealed by their lower cohesive energy and positive phonon modes. More interestingly, these predicted new phases of Be 2 C are all semiconductors and have unusual negative Poisson's ratios (NPRs). If synthesized, 2D Be 2 C materials will have a broad range of applications in electronics and mechanics.

Giant negative Poisson's ratio in two-dimensional V-shaped materials

“…The mechanical parameters including the Young's modulus and Poisson's ratio of the MX monolayers calculated from first-principles calculations are presented in Table II. The elastic constants satisfy the mechanical stability criteria 39 and 2 11 22 12…”

“…17 After the first realization of 2D auxetic effects in graphene with thermally-induced ripples, 18 a number of 2D materials have been reported to have NPR. [19][20][21][22][23][24][25][26][27][28][29][30] For example, monolayer black phosphorene with a buckled structure was predicted to have NPR of about -0.027 which has been confirmed in experiments. 11,19 Generally, the auxetic behaviors of 2D materials are correlated to the geometric structures, the deformation mechanisms of the materials dominated by the inter-atomic interaction.…”

“…Some special geometric configurations, such as re-entrant and hinged structures, have inherent auxetic features independent of atomic interactions. [20][21][22][23][24][25][26][27][28] While in other cases, the auxetic behaviors are relevant to the electronic structures of 2D materials which determine the atomic interactions, rather than the geometry. [29][30][31][32] Strong auxetic effect will greatly improve the mechanical performance of materials, such as dentation resistance or hardness.…”

Towards rational design of low-dimensional material: from structure prediction to molecular engineering

“…而将性能因素添加 到全局搜索结构中的作法有可能会增加搜索的复杂 度. 对于低维材料预测, 特别是二维材料, 厚度、原子 数目、衬底的选择等因素, 都有可能影响搜索的结 果 [38,50,51] . 近年来, 借助包括全局结构搜索、机器学 习 [52] 等在内的自动化的、高效的算法与工具, 可以在 一定程度上提高结构预测的效率.…”

Auxetic two-dimensional transition metal selenides and halides

“…In general, NPR is induced by some specific microstructure morphologies, including re-entrant structure 9,12 , polymetric structure 1,10 , chiral structure 11 , star-shape structure 11 , and so on. Very recently, two-dimensional (2D) crystalline auxetic materials have attracted great attention, and auxetic effects have been reported in various existing or predicted 2D materials [13][14][15][16][17][18][19][20] . In most of the predicted auxetic 2D materials, the NPR is due to pure geometric effect.…”