Ab-initio study of optical response properties of nonstoichiometric lithium-hydride and sodium-fluoride clusters Original Research Article

Structural and optical response properties of LinHn−m and NanFn−m (n=2–6, m=1,2) clusters containing one- and two-excess electrons are studied using ab-initio methods accounting for electron correlation. The common feature of the optical response obtained for the most stable structures of NanFn−1 (n=2–6) clusters is the appearance of a dominant intense transition in the infrared regime independently whether the single excess electron is localized at the cuboid corner vacancy (surface F-center) or at the external atom attached to the filled cuboid. In contrast, LinHn−1 (n=2–6) clusters exhibit substantially different spectroscopic patterns with respect to halides also for the cases with the common structural properties. Optical response features of LinHn−2 (n=3–6) clusters with two-excess electrons are characterized by dominant transitions in the visible regime reflecting segregation in “metallic” and ionic parts. In contrast, NanFn−2 (n=3–6) can be divided according to their optical and structural properties into cuboid “lattice” defect species (Na4F2, Na6F4) and segregated metallic-ionic systems. For the former, the intense transitions occur in the infrared-visible, and for the latter only in the visible regime. It will be shown that the calculated absorption patterns are excellent fingerprints of structural and bonding properties.