<b><i>Ab initio</i></b>studies of the (100), (110), and (111) surfaces of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">CoSi</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Based on the ultrasoft pseudopotential technique of the Vienna ab initio simulation package, we performed ab initio calculations for the (100), (110), and (111) surfaces of ${\mathrm{CoSi}}_{2}$ within the framework of the generalized gradient approximation. Surface energies were derived from the total energies as well as estimated from simple models. Relaxed surface geometries were determined for the $(1\ifmmode\times\else\texttimes\fi{}1)$ surfaces by force minimization. For the (100) surface a proposed $\sqrt{2}\ifmmode\times\else\texttimes\fi{}\sqrt{2}$ reconstruction was investigated that, however, is not stable. Energetical results as well as simulated scanning tunneling images strongly indicate that the reconstruction does not exist. The band structures show a number of surface states, in particular, in gaps of the projected bulk bands at and above Fermi energy for the (100) and (110) surface. For the Si-Co-Si terminated (111) surface, however, only two Si-like surface bands are found. Some surface states are analyzed in terms of density contours revealing covalent Co-Si bonding and coupling to deeper layers. Work functions are also provided.