Electronic structure ofLi12Si7

Ab initio localized-spherical-wave calculations on crystalline ${\mathrm{Li}}_{12}$${\mathrm{Si}}_{7}$ are reported. The crystal consists of two one-dimensional units, (${\mathrm{Li}}_{6}$${\mathrm{Si}}_{5}$${)}_{\mathrm{\ensuremath{\infty}}}$ and (${\mathrm{Li}}_{12}$${\mathrm{Si}}_{4}$${)}_{\mathrm{\ensuremath{\infty}}}$, that contain five-membered Si rings and four-membered Si stars, respectively. In the density of states the region below -5 eV is largely determined by the local ringlike and starlike arrangements of the Si atoms; above -5 eV there is a signature of delocalization of states across the subunits. Additional calculations on the separate units show that ${\mathrm{Li}}_{12}$${\mathrm{Si}}_{7}$ can be described as [${\mathrm{Li}}_{12}$${\mathrm{Si}}_{4}$${]}^{4+}$[${\mathrm{Li}}_{6}$${\mathrm{Si}}_{5}$${]}_{2}^{2\mathrm{\ensuremath{-}}}$ where the charge transfer places the Fermi energy in the gaps of the aromatic subunits. A simple molecular orbital model is presented in order to rationalize the occurrence of these gaps. A short comparison to the theoretical density of states of liquid ${\mathrm{Li}}_{12}$${\mathrm{Si}}_{7}$ is also presented. \textcopyright{}1996 The American Physical Society.