An ab initio study based on an ultrasoft pseudopotential approach is performed for ${\mathrm{CoSi}}_{2}(111)/\mathrm{Si}(111)$ interfaces. Four different geometries A7, B7, A8, and B8 according to sevenfold and eightfold nearest-neighbor Co-Si interface bonding and two types of stacking are calculated. Several formulations of interface energies are considered with and without strain of the ${\mathrm{CoSi}}_{2}$ block. The interface energy involving free surfaces without strain is chosen for deciding the stability of the interface structures. After geometry relaxation type A8 with an interface energy of 0.39 eV is the most stable interface, being more stable by 0.04, 0.06, and 0.10 eV than types B8, A7, and B7, correspondingly. By taking into account the strain energy of ${\mathrm{CoSi}}_{2}$ a critical thickness of 150 \AA{} of ${\mathrm{CoSi}}_{2}$ is estimated. The relaxed interlayer spacings and atomic positions reveal strong bonding effects for interface structures A8 and B8. The good agreement of our data for structures A8 and B8 with experiment supports the view that experimentally grown interfaces are of the eightfold-coordinated type. An analysis of the electronic structure is made in terms of interface localized states. Strongly localized states are found in the Si gap of A8 and B8 interfaces. Planar-averaged densities for selected states are discussed for types A7 and A8. From the averaged metal-induced gap electron density, we derive decay lengths in Si which are significantly different, namely, about 3 \AA{} for types A7 and B7 but much longer ranged for types A8 (about 5 \AA{}) and B8 (about 4 \AA{}). Schottky barriers for p-doped Si are derived in two different ways. The two sets of data agree reasonably showing significantly larger barrier heights for types A7 and B7 in comparison to their eightfold counterparts. The barrier heights are generally smaller than the experimentally accepted value. A correction is estimated based on quasiparticle concepts.