Coupling of lattice distortions to bands near the Fermi level in ABC compounds from first principles

ABC intermetallic compounds exhibit a rich variety of crystal structures and electronic properties. In this work, we use first-principles calculations to elucidate the coupling of lattice distortions to the electronic bands near the Fermi level in a family of hexagonal P6mmc and P63mc ABC compounds, where A is a rare earth, B is a transition metal and C is a main group element. In particular, we have shown that in certain compounds in this family, a polar distortion that buckles the honeycomb layers can open a gap at the Fermi level. In addition, we show that epitaxial strain couples to the bands near the Fermi level directly, as well indirectly through polarization-strain coupling. These results have a number of implications for the targeted design of functional properties in these class of materials, which have been previously proposed as novel candidate ferroelectrics and piezoelectrics.