Adsorption of O and CO on Ir(100) from first principles

The adsorption of O and CO on Iridium (100) surface with different coverages (I similar to = 1.0, 0.5, 0.25 monolayer (ML)) is studied using density functional theory (DFT). The most energetically preferred site of adsorption for O is found to be the bridge site. However, the top site is the preferred one for CO at coverages of 0.25 ML and 0.5 ML. Oxygen adsorbed on the bridge site at 0.25 ML and 0.5 ML coverages causes a row pairing. A missing row reconstruction appears in the case of 0.25 ML coverage. We find that the adsorption of O (CO) on Ir(100) surface causes disruptions of Ir-Ir bonds in the metal, which reduces (increases) the Ir-Ir bond length.