Development of interatomic potentials for the complex binary compound Sb2Te3 and the prediction of thermal conductivity

Molecular dynamics (MD) simulation has emerged as a powerful predictive tool to study mechanical and thermal properties of materials, without the requirement for any fitting parameter inputs such as phonon relaxation time. However, the lack of suitable interatomic potentials for many complex materials greatly prohibits effective use of MD simulations to investigate properties of bulk materials and nanostructures. In this paper, we use the method of fitting to an ab initio energy surface to develop interatomic potential parameters for the complex binary material antimony telluride, which has important applications in thermoelectric energy generation. Density-functional theory is used to calculate the ground-state electronic structure of the ${\mathrm{Sb}}₂{\mathrm{Te}}₃$ crystal, following which the total energies of a series of artificially distorted lattice configurations are calculated to create the energy surface. A Morse potential functional form is fitted to the energy surface and experimental data, and the parameters are used to calculate the bulk crystal properties and phonon spectra using lattice dynamics. Our parameters are able to reproduce the lattice structure, elastic constants, and acoustic phonon dispersion in good agreement with experimental data. MD simulations are performed using the fitted potential to calculate the thermal conductivity of bulk ${\mathrm{Sb}}₂{\mathrm{Te}}₃$ using the Green-Kubo method. The predicted thermal conductivity shows a $1/T$ variation in both in-plane and cross-plane directions with the results in the range of experimental measurements. Frequency domain normal mode analysis is used to calculate the modal phonon relaxation times and the accumulation of thermal conductivity with respect to phonon mean free paths. The results show that phonons with mean free paths between 3 and 100 nm contribute to 80% of the total cross-plane thermal conductivity.