Electronic properties of alkali-metal—gold compounds

Self-consistent relativistic band-structure calculations have been performed for the alkali-metal—gold compounds, $M\mathrm{Au}$ ($M=\mathrm{L}\mathrm{i},\mathrm{N}\mathrm{a},\mathrm{K},\mathrm{R}\mathrm{b}$, and $\mathrm{Cs}$) in the CsCl structure. CsAu and RbAu are semiconductors at normal pressure, whereas the other compounds—in the assumed CsCl structure—are metallic. Total-energy calculations are used to derive equilibrium volumes, bulk moduli, and heats of formation. The calculations suggest that RbAu undergoes an insulator-metal transition at a moderate pressure, $\approx 30$ kbar. KAu is the metallic compound in the series which is "closest" to being an insulator; a uniform expansion corresponding to a pressure of $\approx -30\mathrm{}$ kbar would cause a metal-insulator transition.