We revisit the theoretical description of the F color center in lithium fluoride employing advanced complementary ab initio techniques. We compare the results from periodic supercell calculations involving density-functional theory (DFT) and post-DFT techniques with those from the embedded-cluster approach involving quantumchemical many-electron wave-function techniques. These alternative approaches yield results in good agreement with each other and with the experimental data provided that correlation effects are properly taken into account.
Rainbow scattering for grazing-angle incidence of atoms at surfaces along low-indexed channeling directions provides a sensitive probe of quasistatic atom-surface potentials. The dependence of the rainbow angle on the kinetic energy for the projectile motion perpendicular to the surface, E Ќ , varies with the electronic structure of the projectile as well as the crystallographic face of the aluminum surface. Comparison between experiment and classical Monte Carlo trajectory simulations demonstrates that the superposition of binary atom-atom potentials fails to adequately represent the equipotential surfaces. Ab initio atom-surface potentials based on density-functional theory are required to reach satisfactory agreement with experiment.
We revisit the well-known Mollwo-Ivey relation that describes the "universal" dependence of the absorption energies of F-type color centers on the lattice constant a of the alkali-halide crystals, E abs ∝ a −n . We perform both state-of-the-art ab-initio Quantum Chemistry and post-DFT calculations of F-center absorption spectra. By "tuning" independently the lattice constant and the atomic species we show that the scaling of the lattice constant alone (keeping the elements fixed) would yield n = 2 in agreement with the "particle-in-the-box" model. Keeping the lattice constant fixed and changing the atomic species enables us to quantify the ion-size effects which are shown to be responsible for the exponent n ≈ 1.8.2
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