The large‐deformation energetics of a single molecular chain of the rod‐like polyimide PMDA‐PDA was investigated using DFT, ab initio MO and semi‐empirical MO methods. The force/displacement curves were calculated from tensile testing simulations along the axis of the molecular chain, allowing a discussion of the distribution and change of local strain of the molecular chain. The deformation behavior of a single PMDA‐PDA molecular chain under finite deformations as functions of bending angle and dihedral angle between PMDA and PDA groups are compared. It is found that the semi‐empirical MO calculations provide sufficient accuracy to express the energetics of large deformations except for compressive deformation.
