Electronic band structure calculations of Nowotny “chimney-ladder” isostructural ruthenium and osmium silicides and related germanides have been performed by the linear muffin-tin orbital method within the local density approximation. Both silicides have been found to be direct gap semiconductors with energy gaps of 0.41 and 0.95 eV in ${\mathrm{Ru}}_2{\mathrm{Si}}_3$ and ${\mathrm{Os}}_2{\mathrm{Si}}_3,$ while the band gaps in the germanides have a competitive indirect-direct character with gaps of about 0.3 and 0.9 eV in ${\mathrm{Ru}}_2{\mathrm{Ge}}_3$ and ${\mathrm{Os}}_2{\mathrm{Ge}}_3,$ respectively.

• Received 4 June 1999

DOI:https://doi.org/10.1103/PhysRevB.60.16494