First-principles molecular orbital calculation of electron energy-loss near-edge structures of alpha-quartz

We report results of first-principles molecular orbital calculations using the discrete-variational (DV)-X alpha method on a model cluster of alpha-quartz (Si5O16)(12-). Self-consistent calculations of the cluster which include a half-filled core hole, i.e. at Slater's transition state, are made in order to evaluate the effect arising from the presence of a core hole associated with the electron energy-loss process. The presence of a half-filled Si-2p core hole does not change the unoccupied Si-3s/3d partial density of states (PDOS) significantly. On the other hand, a remarkable core hole effect appears on 0-2p PDOS when a half-filled O-1s hole is introduced. The calculated PDOS at the transition states is in good agreement with the electron energy-loss near-edge structures (ELNES) at both the Si-L(23) edge and O-K edge. Absolute transition energies at both edges are also reproduced to within an error of 3 eV when spin-polarization during the transition is taken into account. The photoabsorption cross sections (PACS) are calculated from first principles and are compared with the PDOS for the corresponding electric dipole transitions. The difference between the PACS and the PDOS is found to be small at both the ground state and the Slater's transition state in the present calculation.