First-Principles Study of the α-β Phase Transition of Ferroelectric Poly(vinylidene difluoride): Observation of Multiple Transition Pathways

Transition routes from the alpha (nonpolar) phase to the beta (polar) phase of polyvinylidene difluoride (PVDF) are investigated by first-principles simulation methods. Among various possible routes, including complex torsional and rotational motions, we propose two prototypical transition routes and identify important intermediate structures along each transition pathway using the generalized solid-state nudged elastic band (G-SSNEB) method. The effect of the external electric field and mechanical drawing on the transition behavior is investigated by estimating electric enthalpy and stress tensors. Finite-temperature ab initio molecular dynamics (AIMD) simulations and stress tensor analysis reveal the possibility of enhancement of the crystallinity under hydrodynamic compression.