We have investigated the atomic structure, electronic states, and stress tensor for a Ge/Si(113)-2×2 surface by using first-principles total energy calculations. We have found that the model made up of tilted pentamers with an interstitial atom and rebonded atoms has the lowest surface energy of the models employed. The local density of states calculated for this surface provides a satisfactory description of recent scanning tunneling microscope images. Furthermore, it has been found that the surface stress is quite anisotropic, resulting in anisotropic growth of Ge films on Si(113).