Definition of bond paths and bond directions in terms of the molecular charge distribution

Abstract

The virial partitioning of a molecular electronic charge distribution, ρ(r), divides a molecule into a collection of chemically identifiable atomic-like fragments. When two fragments interact strongly the distribution of charge in the region between their nuclei contains a saddle point [Formula: see text] The gradient paths (paths of steepest ascent through ρ(r), as traced by the vectors [Formula: see text]) which terminate at this internuclear saddle point, define the virial partitioning surface which lies between the fragments. The two gradient paths which originate at the internuclear saddle point and terminate at each of the fragment nuclei define a bond path: the path which follows the ridge of maximum charge density between a pair of bonded nuclei. When the internuclear axis does not coincide with a symmetry axis, the internuclear stationary point will, in general, lie off the axis, and the bond path joining the nuclei will deviate or curve from this axis. The magnitude and direction of this 'bond curvature' as determined by the bond path agrees well with chemical expectations.