First-principles calculations of the electronic band structure for the layer-type compounds $2H-\mathrm{Nb}{\mathrm{Se}}_2$ and $2H-\mathrm{Mo}{\mathrm{S}}_2$ predict a 1-eV hybridization gap within the $d_{z^2}$ and $d_{\mathrm{xy}}$, $d_{x^2-y^2}$ manifolds of the metal-atom $4d$ bands. This produces a narrow (∼ 1 eV) filled valence band in $2H-\mathrm{Mo}{\mathrm{S}}_2$ and a half-filled conduction band in $2H-\mathrm{Nb}{\mathrm{Se}}_2$, in agreement with electrical, optical, and recent photoemission date.

• Received 16 March 1973

DOI:https://doi.org/10.1103/PhysRevLett.30.784