Theoretical evidence for the Peierls transition in NbO 2

We show by advanced electronic structure calculations that ${\mathrm{NbO}}_{2}$ essentially is a Peierls-type material. After simulating the rutile as well as the body-centered tetragonal phase with the Bethe-Salpeter equation, we are able to reproduce the experimental values for the electronic properties without adding correlations. Our calculation includes only excitonic corrections and no further interactions. The principal indirect gap is between $N$ and $\mathrm{\ensuremath{\Gamma}}$ and is found to be 0.98 eV, the direct gap at the $\mathrm{\ensuremath{\Gamma}}$ point amounts to 1.35 eV. We found the rutile structure to be anisotropic, with nesting vectors in the Fermi surfaces in the $\mathrm{\ensuremath{\Gamma}}MAZ$ and $\mathrm{\ensuremath{\Gamma}}XRZ$ planes.