We have investigated the atomic structure and electronic states for the Ge/Si(113)-2 x 2 surface using first-principles total energy calculations. We have found that the model made up of alternating [1 (1) over bar0]-oriented rows of rebonded atoms and tilted pentamers of five atoms with an interstitial atom has the lowest surface energy of the models employed. Furthermore, the local density of states calculated for this surface provides a satisfactory description of recent scanning tunneling microscope images. (C) 2003 Elsevier Science B.V. All rights reserved.