Molecular dynamics study of two dimensional silicon dioxides with in-plane negative Poisson's ratio

In the present work, the mechanical properties, in particular, the Poisson's ratio of four two-dimensional silica structures, called here α,β,γ, and δ are studied by means of molecular dynamics simulations. The α structure has been synthesized experimentally and the others have been reported as the most stable low-energy structures that reveal in-plane negative Poisson's ratio based on the first principles calculations. Among these structures, β-silica exhibits the largest in-plane negative Poisson's ratio which is 2-4 times higher than penta-graphene. Our results illustrate that the classical molecular dynamics simulation reproduces results in agreement with those of the first principles calculations. Consequently, it enables us to study the mechanical responses of considerably larger systems at finite temperatures in contrast to the ab initio simulations. Furthermore, we systematically study the temperature effects on the stability and mechanical properties of these two-dimensional silica structures, up to their rupture points. It is found that the mechanical properties of these structures vary significantly with temperature, and γ-silica exhibits a switchable behavior in its Poisson's ratio with temperature.