Relation between Electronic Structure andTcin Binary and Ternary Molybdenum Chalcogenides

Localized orbital calculations are presented for the electronic structure of Chevrelphase molybdenum chalcogenides. Densities of states at the Fermi energy, $N\left(E_{\mathrm{F}}\right)$, are found to depend sensitively on the modification of intercluster interactions because of lattice distortions introduced by the ternary component. Calculated $N\left(E_{\mathrm{F}}\right)$ values in ${\mathrm{Mo}}_6$ ${\mathrm{S}}_8$, Pb${\mathrm{Mo}}_6$ ${\mathrm{S}}_8$, ${\mathrm{Mo}}_6$ ${\mathrm{Se}}_8$, and Pb${\mathrm{Mo}}_6$ ${\mathrm{Se}}_8$ are 0.5, 1.7, 1.1, and 0.9 states/(spin Mo-atom eV), respectively, and show a strong correlation with $T_c$. States near to $E_{\mathrm{F}}$ are strongly confined within ${\mathrm{Mo}}_6$ octahedra.