DV-Xα Calculation and Ultraviolet Photoelectron Spectra of Gold Trichloride-Graphite Intercalation Compound (AuCl₃-GIC)

We investigate the electronic structure of AuCl₃ graphite intercalation compounds by means of discrete variational (DV)-Xα molecular orbital calculation and ultraviolet photoelectron spectra (UPS). DV-Xα calculation of the Au₂Cl₆ intercalate reveals the importance of relativistic effect due to the presence of heavy Au atoms. The terminal Cl 3p orbital contributes mainly to the lowest unoccupied molecular orbital (LUMO) of Au₂Cl₆ molecule in addition to the minor contribution of the Au 5d component. The calculation of (Au₂Cl₆)^-0.5, which is considered to be intercalate species realized in graphitic galleries through charge transfer from graphite, suggests that the Au₂Cl₆ intercalate band is located at around the Fermi level E_F as well as the graphitic π-band. As a consequence, the density of states at E_F is 2-3 times larger than that expected only by the graphitic π-band, which is consistent with optical reflectance, magnetic susceptibility, and the electronic specific heat. The small hump around E_F in the UPS of AuCl₃-GIC is considered to be associated with the intercalate band. The overlap population analysis suggests the bonds between gold and chlorine atoms in Au₂Cl₆ become weaker when the 0.5 electron transfer from graphitic π-band to Au₂Cl₆ molecule. Therefore, the interatomic distances in the Au₂Cl₆ molecule are found to become elongated, consistent with the experimental results of the Raman spectra.