Combining the Static and Dynamic Approaches to Mechanical Property Recognition for Coumarin Polymorphic Forms

The effective methodology for predicting the mechanical properties of polymorphic forms of crystals was proposed. It consists of combining static and dynamic approaches. The first one is based on the calculated stiffness tensor and allows one to draw conclusions on crystal flexibility or stiffness. The second approach relies on the results of a virtual tensile/contraction test, which allows judging on the elasticity or plasticity of a crystal along certain crystallographic axes. The effectiveness of the methodology is exemplified by theoretical estimations made for polymorphic forms I (elastic) and II (plastic) of coumarin crystals. The anisotropy of their mechanical properties was analyzed theoretically for the first time, based on the virtual stretching and virtual contraction of the crystal structure. The comparison of the calculated stiffness tensors, the anisotropy of elastic moduli in the equilibrium state, and the analysis of the influence of noncovalent bonds on the uniaxial and hydrostatic compressibility for two polymorphic forms were performed. Such a strategy can complement the understanding of how important the consideration of static and dynamic properties is for the theoretical predictions of mechanical behavior of molecular crystals.