Motivated by our recent scanning tunneling microscopy measurements on $\text{Re}\left(11\overline{2}1\right)$ that, depending on the nature of the adsorbate, showed the formation of distinct facets when the substrate is annealed to elevated temperatures, we used density-functional theory to explore why faceting of $\text{Re}\left(11\overline{2}1\right)$ induced by ${\text{NH}}_3$ is different from that by ${\text{O}}_2$. Our calculations indicate that nitrogen adsorption causes two-sided ridges, combining $\left(13\overline{4}2\right)$ and $\left(31\overline{4}2\right)$ faces, to become thermodynamically favored at temperatures below 1080 K while oxygen adsorption below 1130 K leads to four-sided pyramids exhibiting $\left(10\overline{1}0\right)$, $\left(01\overline{1}0\right)$, $\left(10\overline{1}1\right)$, and $\left(01\overline{1}1\right)$ faces.

• Received 27 March 2009

DOI:https://doi.org/10.1103/PhysRevB.79.132107