NEUTRAL ATOMS IN IONIC LATTICES - STUDY OF KCL-AG-0

To obtain better insight into the optical and EPR properties exhibited by the KCl:Ag-0 system, MS-X alpha and self-consistent charge extende d Huckel calculations as a function of the metal-ligand distance, R, w ere carried out. As calculations on simple AgCl66- clusters led to inc onsistent results (underlining that Ag-0 in KCl is a kind of shallow i mpurity), studies on (AgCl6K12Cl8)(2-) and (AgCl6K12Cl8K6Cl24K24)(4+) were performed. The present results indicate that the stability of the Ag-0 center in KCl is related to a strong outward relaxation (of abou t 20%) of ligands, supporting previous analysis of the isotropic super hyperfine constant. Also, they explain the existence of one (and not t wo) charge-transfer transitions in the V-UV region, in spite of the ze ro nominal charge of the silver atom. As a curious feature, the e(g) and t(2g) levels are practically degenerate and exhibit a pure 4d cha racter. This fact thus explains why the spin-orbit splitting seen in t he 4d(10) 5s --> 4d(9) 5s(2) transitions is the same as in free Ag-0. Although the a(1g) level coming from 5s(Ag) is rather localized, it i s shown that in the resonant t(1u) level [arising from 5p(Ag)] the el ectron spends only 25% of its time on silver. This different behavior is related to the reduction of the 5s --> 5p transition energy on pass ing from free atom to KCl:Ag-0, which is in agreement with experimenta l findings. (C) 1997 John Wiley & Sons, Inc.