AB-INITIO STUDY OF STRUCTURAL AND OPTICAL-RESPONSE PROPERTIES OF EXCESS-ELECTRON LITHIUM-HYDRIDE AND SODIUM-FLUORIDE CLUSTERS

Structural and optical response properties of stoichiometric small Lin Hn and NanFn and non-stoichiometric LinHn and NanFm (n - m = 1, 2, 3, 8) clusters containing single and multiple excess electrons are studie d using ab initio methods accounting for electron correlation. We show that calculated absorption patterns are excellent fingerprints of str uctural and bonding properties. The optical response of NanFn-1 (n = 2 -6) clusters is characterized by the common feature that is the appear ance of a dominant intense transition in the infrared regime, independ ently whether the excess electron is localized at the cuboid corner va cancy or at the external atom attached to the filled cuboid. In contra st, LinHn-1 (n = 2-6) clusters exhibit substantially different spectro scopic patterns with respect to halides also for nuclearities with ana logous structures. NanFn-2 (n = 3-6) clusters containing two excess el ectrons can be divided according to their optical and structural prope rties into cuboid ''lattice'' defect species (Na4F2, Na6F4) and segreg ated metallic-ionic systems (Na3F, Na5F3). For the former, intense tra nsitions are found in the infrared-visible region, and for the latter only in the visible regime. LinHn-2 (n = 3-6) clusters exhibit common optical response features with dominant transitions in the visible reg ime which is characteristic for segregated metallic-ionic systems. Gro und and excited state properties of above systems are in good agreemen t with available experimental data. Comparison with properties found f or pure alkali-metal clusters allow one to investigate metallization a nd localization processes in finite systems.