THE RELATIVE PERFORMANCE OF THE LOCAL-DENSITY APPROXIMATION AND GRADIENT-CORRECTED DENSITY-FUNCTIONAL THEORY FOR COMPUTING METAL-LIGAND DISTANCES IN WERNER-TYPE AND ORGANOMETALLIC COMPLEXES

Optimized metal-ligand (M-L) bond lengths for 17 classical Werner-type transition-metal complexes were calculated using the local density ap proximation (LDA) and a gradient-corrected (GC) extension. GCs lengthe n the bonds by between 0.02 and 0.09 Angstrom relative to the LDA resu lts. The latter range from 0.02 Angstrom shorter than observed to 0.05 Angstrom longer, while the GC data range from exact agreement with ex periment to some 0.12 Angstrom too long. The LDA rms deviation is 0.02 5 Angstrom, compared to the GC error of 0.070 Angstrom. In contrast, d ata from the literature for organometallic species show that the LDA g ives systematically too short M-L distances and GCs lead to a better a greement with experiment. The relative performance of LDA and GC funct ionals reflects the qualitatively different chemistries of organometal lic and Werner-type complexes. The magnitude of the GC bond-length exp ansion for the latter correlates with the ionicity of the M-L interact ion. (C) 1997 John Wiley & Sons, Inc.