First principles high-throughput search of ferroelectric topological insulators

Ferroelectric topological insulators, insulating materials with a spontaneous and switchable macroscopic polarization, where a small band gap is opened in the presence of spin-orbit interaction, are extremely rare. In this context, the prediction of small band gap ferroelectrics is limited by the well-known underestimation of the density functional theory band gap obtained through semi-local functionals such as the generalized gradient approximation. However, hybrid functionals include a fraction of exact exchange, and tend to correct the underestimation of the band gap, resulting in a band gap prediction comparable to experimental measurements. In this work, we use first-principles calculations to perform a high-throughput search of ferroelectric topological insulators in the Materials Project database. We start by identifying all materials in the database possessing a polar and a nonpolar reference structure connected by a continuous symmetry distortion. Unlike previous works, where only materials with both polar and nonpolar phases insinuating are considered, we focus on cases where the polar phase is metallic. Next, we perform higher theory-level calculations with (1) hybrid functionals, and (2) hybrid functionals and spin-orbit interaction to identify small band gap ferroelectrics and ferroelectric topological insulators. For the materials identified we calculate topological invariants and electronic polarizations. This work is supported by ANID FONDECYT Regular 1220986.