2023 Spring Physics Colloquium Series: Prof. Q. Zhu

Recently, some organic crystals have been found to be surprisingly flexible by undergoing a large extent of elastic or plastic deformation upon mechanical loads. Despite the increasing experimental reports on such mechanically flexible crystals, this phenomenon has never been reproduced in numerical simulation and thus there is no atomistic mechanism to explain its physical origin. Using three recently reported naphthalene diimide derivatives as the examples, we performed the first direct molecular dynamics simulation to model their mechanical behaviors from brittle fracture to elastic/plastic deformation upon mechanical bending. Our simulation reveals that molecular rotational freedom is the key factor to determine the crystal's mechanical response. Furthermore, we propose to use spherical harmonic transform and first-principles crystal structure prediction to screen and design new mechanically flexible candidates with better functionalities. The combination of different computational techniques is promising to harvest new bendable organics for future technological applications.