Abstract
Density functional calculations are reported for , , and supercells representing . We find that the H positions are soft in the sense that displacements along the hexagonal axis are energetically favored for some orderings and displacement patterns. This is discussed in relation to the anomalous structural and nuclear magnetic resonance data reported for this compound. The mechanism for this softness is related to the electronic structure, specifically coupling to strongly hybridized bands occurring near the Fermi energy. In particular, certain patterns of H shifts along the axis strongly mix and bands, leading to strong coupling between these shifts and bands at the Fermi energy and instabilities of phonons with these displacement patterns.
1 More- Received 27 February 2007
DOI:https://doi.org/10.1103/PhysRevB.76.075120
©2007 American Physical Society