Monoatomic X- (X = O, S) chalcogen centers in MZ (M = Na, K, Rb and Z = Cl, Br, I) alkali halide lattices were investigated within the framework of density functional theory with the principal aim to establish defect models. In electron paramagnetic resonance experiments, X- defects with tetragonal, orthorhombic, and monoclinic g-tensor symmetry were observed. Here, models in which X- replaced a single halide ion, with a next-nearest neighbor and a nearest-neighbor halide vacancy, were validated for the X- centers with tetragonal and orthorhombic symmetry, respectively. As such defect models were extended, the ability to reproduce experimental data was a stringent test for various computational approaches. Cluster in vacuo and embedded cluster schemes were used to calculate energy and electron paramagnetic resonance parameters for the 2 vacancy configurations. The final attribution of a defect structure was based upon the qualitative and quantitative reproduction of experimental g and (super)hyperfine tensors.X- (X = O, S) Ions in Alkali Halide Lattices Through Density Functional Calculations - Substitutional Defect Models. F.Stevens, H.Vrielinck, V.Van Speybroeck, E.Pauwels, F.Callens, M.Waroquier: Journal of Physical Chemistry B, 2006, 110[16], 8204-12