Peierls distortion in hexagonalYH3

Abstract

A pseudopotential local-density calculation is performed for ${\mathrm{YH}}_3$ to study the unusual hydrogen displacements previously found in neutron diffraction. These displacements are Peierls distortions associated with (hydrogen) lattice instability in this 3D system. The wave vector of these displacements is close to the vector connecting the electron and hole pockets in the undistorted system. With other electron and hole pockets at Γ that still overlap after distortion, the possibility of the existence of an excitonic insulator phase will be discussed.