Abstract
The cluster compounds KNa3In9 [K2Na6(In12)(In)6] and Na2In [(Na)8(In4)], which contain In12 icosahedra interbridged by 4-bonded In atoms and isolated In4 tetrahedra, respectively, both have classical closed-shell electronic configurations but show metallic transport properties. These contrasts have been studied by means of first-principles density functional methods (LMTO-ASA). Several bands cross the Fermi level in both compounds, consistent with their metallic properties. In KNa3In9, the metal atom framework alone is sufficient to generate a metallic characteristic. The alkali-metal s and indium p orbitals mix considerably in both phases, providing for substantial covalent contributions to their stabilities as well as bands crossing Ef. The participation of Na atoms in the 3D bonding networks is more striking in cation-richer Na2In than in KNa3In9.
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