Computing the Ideal Strength of Atomically Thin Materials From First Principles

Eric Isaacs, Columbia University

Photo of Eric Isaacs

Recent ab initio calculations suggest that the ideal strength of graphene, the world’s strongest material, is limited by a finite wave-vector phonon instability [1]. In order to understand the origin and generality of phonon instabilities in two-dimensional crystals, we investigate the ideal strength of other monolayer materials including boron nitride (BN), molybdenum disulfide (MoS2), graphane, and silicene with density functional theory calculations. We find a soft phonon mode at the K-point of the Brillouin zone for BN, MoS2, and graphane under equibiaxial tensile strain, leading to mechanical failure for BN and MoS2. While the distortion of BN and graphane is similar to that of graphene, MoS2 undergoes a more complex phase transition with both in- and out-of-plane atomic displacements. We find that the structural transformations for BN, MoS2, and graphane do not result in the opening of a band gap, which indicates that Fermi surface nesting cannot be a universal explanation for phonon instabilities in monolayer materials.

[1] C.A. Marianetti and H.G. Yevick, Phys. Rev. Lett. 105, 245502 (2010).

Abstract Author(s): Eric B. Isaacs and Chris A. MarianettiDepartment of Applied Physics and Applied Mathematics, Columbia University