Atomic interaction line

Now we focus on the gradient paths, which do not terminate at a nucleus, but rather link two nuclei. For example, the bond critical point between C and H in Figure 6.14 is the origin of two gradient paths. One gradient path terminates at the hydrogen nucleus, the other at the carbon nucleus. This pair of gradient paths is called an atomic interaction line. It is found... 

Bond critical points represent extremes of electronic density. For this reason, these points are located in space where the gradient vector V p vanishes. Then the two gradient paths, each of which starts at the bond critical point and ends at a nucleus, will be the atomic interaction line. When all the forces on all the nuclei vanish, the atomic interaction line represents a bond path. In practice, this line connects two nuclei which can consequently be called bonded [5]. In terms of topological analysis of the electron density, these critical points and paths of maximum electron density (atomic interaction lines) yield a molecular graph, which is a good representation of the bonding interactions. 

The sum in this equation runs over the surfaces shared with atoms bonded to n, the atoms linked to 2 by atomic interaction lines. This expression for the force acting on an atom provides the physical basis for the model in which a molecule is viewed as a set of interacting atoms. It isolates, through the definition of structure, the set of atomic interactions which determines the force acting on each atom in a molecule for any configuration of the nuclei. 

An atomic surface S(H, r) is, in general, composed of a number of interatomic surfaces, there being one such surface for each atom O linked to H by an atomic interaction line or, in the case of a bound system, by a bond path. That is. 

The requirements of binding, as viewed through the electrostatic theorem, emphasize the existence of an atomic interaction line as a necessary condition for a state to be bound, whether it be at the shared or closed-shell limit of interaction. The differing properties associated with the distributions of electronic charge at the shared and closed-shell limits of interaction are reflected in the differing mechanisms by which the forces on the nuclei are balanced to achieve electrostatic equilibrium in the two cases. 

Cioslowski and Mixon [57] reported atomic interaction lines connecting hydrogen atoms separated by short distances ( /h -h < 2.18 A) in several polycyclic aromatic hydrocarbons (PAHs). These authors describe this interaction as... 

Figure 7 Contour maps of the electron density for the Ne Hio Ne vise. The intersections of the interatomic surfaces with the plane of the diagram are shown for the left half of each molecule, as are the atomic interaction lines. There is a (3, —1) critical point in the density at each intersection of an interaction line with an interatomic surface. The indicated structures are invariant to an increase in pressure.

Electron density plots of trans-Ammne, HN=NH, as relief plots (a) in the plane of symmetry and (b) perpendicular to it, and the same represented as contour line plots (c) and (d). (e) Gradient vector field of the electron density of trans-diimine, HN=NH. (f) Contour plot of the electron density with interatomic surface lines partitioning the molecular space into atomic basins (interatomic surfaces (IAS) and atomic interaction lines overlaid. All plots are based on calculations at the MP2/6-311G level of theory. 

What is the definition of an atomic interaction line (AIL) in AIM theory ... 

Our second example is more clear-cut. The nickel alkyl complex (shown schematically in Figure 12.33(a) and as a crystal structure in (b)) has a Ni (3-H distance that approaches that of covalent Ni(ll) hydrides [73]. Figure 12.33(c) shows part of a Laplacian plot of an experimentally determined electron density distribution in the NiCCH plane. We see atomic interaction lines for Ni—C, C—C, C—H and Ni—H atom pairs,... 

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