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

## TL;DR

A new ReaxFF force field is developed to simulate the recrystallization of bismuth selenide into van der Waals-layered structures under various conditions.

## Contribution

A novel ReaxFF force field for Bi/Se systems enables predictive modeling of vdW-layered Bi2Se3 recrystallization.

## Key findings

- The ReaxFF force field is parameterized using quantum mechanical data on Bi–Se phases and defects.
- Recrystallized vdW materials' stacking and stoichiometry depend on cooling rate and annealing temperature.
- The force field provides a predictive framework for tuning Bi–Se vdW materials through recrystallization.

## Abstract

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.