Structural properties and strain engineering of a BeB2 monolayer from first-principles†
Boron-based two-dimensional materials have extremely rich structures and excellent physical properties. Using a particle-swarm optimization (PSO) method and first-principles calculations, we performed a comprehensive search for the structure of a two-dimensional BeB2 monolayer. We found new configurations with lower energy compared with the previously reported α phase, namely the β, γ, and δ structures. Among those structures, the δ phase is found to have the lowest energy and we examined its dynamic as well as its thermodynamic stabilities. Then through strain engineering, we found a metal–semimetal transition in the α phase (under about 5% biaxial compressive strain) and in the δ phase (under about 3.2% and 7% biaxial tensile strain). As the compressive strain increases to 7%, the BeB2 sheets of the β phase and γ phase strongly twist, becoming more stable than the δ system. More interestingly, we found that Be atoms could penetrate the B atomic layer in the γ system under 2.5% tensile strain. All the predicted effects demonstrate the rich physical properties of the two-dimensional BeB2 monolayer.