Electronic structure of Li12Si7

Ab initio localized-spherical-wave calculations on crystalline Li12Si7 are reported. The crystal consists of two one-dimensional units, (Li6Si5)(infinity) and (Li12Si4)(infinity), 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 Li12Si7 can be described as [Li12Si4](4+)[Li6Si5](2-)(2) 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 Li12Si7 is also presented.