Development of a ReaxFF Reactive Force Field for the Crystallization of van der Waals-Layered Bismuth Selenide

Bismuth selenide (Bi₂Se₃) is a widely studied topological insulator and thermoelectric material whose properties are highly sensitive to crystal quality, defects, and stoichiometry. Recrystallization is an effective method of improving the crystal quality of materials, yet traditional experimental approaches are time-consuming and resource-intensive and often rely on trial and error. This work presents a new Bi/Se ReaxFF force field with the ability to recrystallize bulk Bi₂Se₃ into van der Waals (vdW)-layered phases under various thermal and kinetic conditions. The force field is parameterized using a diverse quantum mechanical data set, which includes formation energies of bulk layered and nonlayered Bi-Se phases, the energy-volume equation of state, point defect formation energies, the composition-dependent energetic stability trends of high-temperature Bi _x Se _y clusters, and amorphous Bi₂Se₃ structures sampled from melt-quench molecular dynamics simulations. Our simulations reveal that structural characteristics of the resulting recrystallized vdW materials, such as stacking order and stoichiometry, depend on melt-quenching processing parameters such as the cooling rate and annealing temperature. This novel force field constitutes a predictive framework for the structural tuning of complex Bi-Se vdW materials through recrystallization conditions, laying a foundation for computational design of a much wider selection of chalcogenides.