Mechanical equilibrium, a prerequisite to unveil auxetic properties in molecular compounds

International audienceThe unique physical properties of auxetic compounds make them very attractive materials. Nevertheless, no synthesised materials known to exhibit negative Poisson’s ratio at the molecular level have been made. One way to explore such compounds is to predict potential candidates prior to their synthesis. To achieve it, multi-atom simulation is a powerful predicting tool. However, the lack of existing systems means that the crucial step of validation cannot be carried out. This paper aims to provide a procedure to predict the auxeticity of proposed molecular systems. The strategy is based on first revealing the determinant step in reaching the mechanical equilibrium of existing isotropic compounds such as polymers, or organic glasses, to compute efficiently mechanical properties. The Poisson’s ratio is found in good agreement with experimental data. The procedure is thus modified to be applied to anisotropic compounds, liquid crystals. The agreement with experimental behaviour allowed us to extrapolate the procedure to potentially auxetic compounds, thus offering great opportunities to reveal auxetic properties prior to the synthesis of the molecules