Understanding ferroelectricity in elemental materials represents a significant paradigm shift in condensed matter physics, challenging the conventional wisdom that spontaneous polarization requires ionic compounds. While lone‐pair electrons have been proposed as a potential key to unlocking this phenomenon, the underlying mechanism governing their formation and redistribution remains elusive. In this study, we employ first‐principles calculations to investigate the electronic structure of a buckled bismuth monolayer, revealing a selective electron occupation phenomenon where valence and conduction band states preferentially localize on distinct atomic sites. Geometric structure analysis combined with a Slater–Koster parameterized tight‐binding approach shows that the buckling distortion induces asymmetric orbital perturbations to the primary manifold, where constructive and destructive interference drives the site‐selective electron occupation. This mechanism provides a unified microscopic picture of directional charge separation that enables ferroelectric switching in an elemental system. Furthermore, we establish the essential role of spin–orbit coupling in stabilizing the buckled structure, thereby explaining the distinct structural energetics between bismuth monolayers and black phosphorus. These insights provide a fundamental understanding of elemental ferroelectricity and suggest promising avenues for designing novel phase‐change materials and nanoscale ferroelectric devices.
Guo et al. (Sun,) studied this question.