Atomistic mechanisms of phase nucleation and propagation in a model two-dimensional system

We present a computational study on the solid-solid phase transition of a model two-dimensional system between hexagonal and square phases under pressure. The atomistic mechanism of phase nucleation and propagation are determined using solid-state Dimer and nudged elastic band (NEB) methods. The Dimer is applied to identify the saddle configurations and NEB is applied to generate the transition minimum energy path (MEP) using the outputs of Dimer. Both the atomic and cell degrees of freedom are used in saddle search, allowing us to capture the critical nuclei with relatively small supercells. It is found that the phase nucleation in the model material is triggered by the localized shear deformation that comes from the relative shift between two adjacent atomic layers. In addition to the conventional layer-by-layer phase propagation, an interesting defect-assisted low barrier propagation path is identified in the hexagonal to square phase transition. The study demonstrates the significance of using the Dimer method in exploring unknown transition paths without a priori assumption. The results of this study also shed light on phase transition mechanisms of other solid-state and colloidal systems.

Automated summary

In this study, a computational investigation was conducted on the solid-solid phase transition of a model two-dimensional system from a hexagonal phase to a square phase under pressure. The atomistic mechanism and propagation method of the phase transition were determined using solid-state Dimer and nudged elastic band (NEB) methods. It was found that the phase nucleation was triggered by localized shear deformation caused by the relative shift between two adjacent atomic layers. Additionally, a defect-assisted low barrier propagation path was identified in the hexagonal to square phase transition. This study highlights the significance of using the Dimer method to explore unknown transition paths and provides insights into phase transition mechanisms of other solid-state and colloidal systems.