AB-INITIO STUDY OF OPTICAL-RESPONSE PROPERTIES OF NONSTOICHIOMETRIC LITHIUM-HYDRIDE AND SODIUM-FLUORIDE CLUSTERS WITH ONE-EXCESS AND 2-EXCESS ELECTRONS

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 abinitio methods accounting for electron correlation. Th e common feature of the optical response obtained for the most stable structures of NanFn-1 (n = 2-6) clusters is the appearance of a domina nt intense transition in the infrared regime independently whether the single excess electron is localized at the cuboid corner vacancy (sur face F-center) or at the external atom attached to the filled cuboid. In contrast, LinHn-1 (n = 2-6) clusters exhibit substantially differen t spectroscopic patterns with respect to halides also for the cases wi th the common structural properties. Optical response features of LinH n-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 div ided according to their optical and structural properties into cuboid ''lattice'' defect species (Na4F2, Na6F4) and segregated metallic-ioni c systems. For the former, the intense transitions occur in the infrar ed-visible, and for the latter only in the visible regime. It will be shown that the calculated absorption patterns are excellent fingerprin ts of structural and bonding properties.