The ideal strength of monolayer materials possessing semimetallic, semiconducting, and insulating ground states is computed using density functional theory. Here we show that, as in graphene, a soft mode occurs at the K-point in BN, graphane, and MoS2, while not in silicene. The transition is first-order in all cases except graphene. In BN and graphane the soft mode corresponds to a Kekul{\'e}-like distortion similar to that of graphene, while MoS2 has a distinct distortion. The phase transitions for BN, graphane, and MoS2 are not associated with the opening of a band gap, which indicates that Fermi surface nesting is not the driving force. We perform an energy decomposition that demonstrates why the soft modes at the K-point are unique and how strain drives the phonon instability.
@article{arxiv.1311.1497,
title = {Ideal strength and phonon instability of strained monolayer materials},
author = {Eric B. Isaacs and Chris A. Marianetti},
journal= {arXiv preprint arXiv:1311.1497},
year = {2014}
}