Analysis of electron density distributions from subsystem density functional theory applied to coordination bonds

We investigate the electron density topologies from a subsystem approach to density-functional theory (DFT) for subsystems connected by coordination bonds in comparison to Kohn-Sham-DFT reference calculations. Reasonable results can be obtained for weak dative bonds as in H3N center dot center dot center dot BH3 or for bonds with a rather ionic character as in TiCl4. Problems occur for dominant covalent bonding contributions. The subsystem approach shows serious deficiencies in cases of fragments with opposite charge. We show how this problem can be overcome by introduction of a long-distance correction to the embedding potential as recently proposed [C. R. Jacob, S. M. Beyhan, L. Visscher, J. Chem. Phys. 126 ( 2007) 234116]. (C) 2008 Elsevier B.V. All rights reserved.