A Si (110) clean surface has been reported to have a 16x2 structure with a pair of pentagons (PP) elemental structure in upper and lower terraces, and the stability of the structure has been explained using density functional theory (DFT). An et al. investigated the 16x2 structure in detail using high-resolution scanning tunneling microscopy (STM) and showed that the number of bright spots corresponding to the PP structure changes from 10 (positive bias) to 8 (negative bias). Togashi et al. investigated the initial oxidation of the 16x2 structure by using STM and showed that some sites in the PP structure were oxidized preferentially. In this study, STM images were simulated using DFT on a flat Si (110)-(8x2) surface of the adatom-tetramer-interstitial (ATI) model. The dependence of the simulated images on the sample bias was consistent with that reported by An et al. for experimentally obtained STM images. The simulated images were well explained by the calculated density of states. These results indicate that the ATI model can explain the atomic configuration of a Si (110)-(16x2) clean surface. Furthermore, STM images of stable O clusters around the elemental pair of pentagons structure in an initially oxidized Si (110)-(16x2) surface were obtained. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.005203jes] All rights reserved.