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AIM theory

Alternatively, we can base our analysis on the electron density, which as we have seen, is readily obtained from the wave function. The advantage of analyzing the electron density is that, unlike the wave function, the electron density is a real observable property of a molecule that, as we will see in Chapter 6, can be obtained from X-ray crystallographic studies. At the present time however, it is usually simpler to obtain the electron density of a molecule from an ab initio calculations rather than determine it experimentally. Because this analysis is based on a real physically observable property of a molecule, this approach appears to be the more fundamental. It is the approach taken by the atoms in molecules (AIM) theory, which we discuss in Chapters 6 and 7, on which we base part of the discussion in Chapters 8 and 9. [Pg.82]

Before discussing the AIM theory, we describe in Chapters 4 and 5 two simple models, the valence shell electron pair (VSEPR) model and the ligand close-packing (LCP) model of molecular geometry. These models are based on a simple qualitative picture of the electron distribution in a molecule, particularly as it influenced by the Pauli principle. [Pg.82]

At the heart of the AIM theory is the definition of an atom as it exists in a molecule. An atom is defined as the union of a nucleus and the atomic basin that the nucleus dominates as an attractor of gradient paths. An atom in a molecule is thus a portion of space bounded by its interatomic surfaces but extending to infinity on its open side. As we have seen, it is convenient to take the 0.001 au envelope of constant density as a practical representation of the surface of the atom on its open or nonbonded side because this surface corresponds approximately to the surface defined by the van der Waals radius of a gas phase molecule. Figure 6.15 shows the sulfur atom in SC12. This atom is bounded by two interatomic surfaces (IAS) and the p = 0.001 au envelope. It is clear that atoms in molecules are not spherical. The well-known space-filling models are an approximation to the shape of an atom as defined by AIM. Unlike the space-filling models, however, the interatomic surfaces are generally not flat and the outer surface is not necessarily a part of a spherical surface. [Pg.151]

These review papers discuss the AIM theory, including the Laplacian and its relationship to the VSEPR model. [Pg.180]

This chapter is based on the VSEPR and LCP models described in Chapters 4 and 5 and on the analysis of electron density distributions by the AIM theory discussed in Chapters 6 and 7. As we have seen, AIM gives us a method for obtaining the properties of atoms in molecules. Throughout the history of chemistry, as we have discussed in earlier chapters, most attention has been focused on the bonds rather than on the atoms in a molecule. In this chapter we will see how we can relate the properties of bonds, such as length and strength, to the quantities we can obtain from AIM. [Pg.181]

The many higher boranes such as B5H9 and BgH 2 are similarly electron deficient and cannot be described by a single Lewis structure. They can often be described in terms of a combination of two- and three-center bonds. Alternatively, their structures can be rationalized by electron-counting schemes such as those proposed by Wade. Analysis of the electron density of these molecules by the AIM method shows that there are bond paths between all adjacent pairs of atoms. So from the point of view of the AIM theory there are bonds between each adjacent pair of atoms, but these cannot all be regarded as Lewis two-center, two-electron bonds as is the case in B2H6. [Pg.197]

So far we have considered the shape of the electron density of a limited inner region of each atom but not of the complete atom. How do we find the shape of the complete atom In other words, how do we find the interatomic surfaces that separate one atom from another and define the size and shape of each atom The atoms in molecules (AIM) theory developed by Bader and coworkers (4) provides a method for doing this. [Pg.274]

The AIM theory, which is solidly based on quantum mechanics, differs from orbital-based theories in that it is based directly on the electron density and interprets this density to provide information on bonding. The density may be obtained experimentally or from theoretical electronic structure calculation. Experimental densities of sufficient quality to be analyzed by the AIM theory can be obtained from low-... [Pg.274]

Comparison between AIM Theory and Conventional Models for Describing Bonding... [Pg.276]

We now compare how the atoms in a molecule and the bonds between them are defined in the AIM theory and in conventional bonding models. [Pg.276]

In contrast, the AIM theory provides a clear definition of an atom in a molecule as a space-filling object, from which all its properties can be obtained. The properties of these atoms are additive to give the corresponding molecular property. [Pg.277]

Clearly the concepts of ionic and covalent character have only an approximate qualitative significance. They cannot be defined and therefore measured in any quantitative way. Although they are widely used terms and have some qualitative usefulness if used carefully they have caused considerable misunderstanding and controversy. The AIM theory does, however, provide properties that we can use to characterize a bond quantitatively, such as the bond critical point density and the atomic charges. It seems reasonable to assume that the strength of a bond depends on both these quantities, increasing as pb and the product of the atomic charges increase. [Pg.277]

The AIM theory provides a clear and rigorous definition of an atom as it exists in a molecule. It is the atomic basin bounded by the interatomic surfaces. The interatomic... [Pg.278]

The concept of a bond has precise meaning only in terms of a given model or theory. In the Lewis model a bond is defined as a shared electron pair. In the valence bond model it is defined as a bonding orbital formed by the overlap of two atomic orbitals. In the AIM theory a bonding interaction is one in which the atoms are connected by a bond path and share an interatomic surface. [Pg.278]

In the early 1970s, Dr. Bader invented the theory of "Atoms in Molecules," otherwise known as AIM theory. This theory links the mathematics of quantum mechanics to the atoms and bonds in a molecule. AIM theory adopts electron density, which is related to the Schrodinger description of the atom, as a starting point to mapping molecules. [Pg.186]

AIM theory provides a physical basis for the theory of Lewis electron pairs and the VSEPR model of molecular geometry. Equipped with computers and computer-generated, three-dimensional electron density maps, scientists are able to view molecules and predict molecular phenomena without even having to get off their chairs ... [Pg.186]

A modem description of a conventional hydrogen bond as well as its older, more accurate definition are based on Bader s theory of atoms in molecules (AIM theory) [4]. Bader considers matter a distribution of charge in real space of point-like nuclei embedded in the diffuse density of electron charge, p(r). All the properties of matter are manifested in the charge distribution and the topology... [Pg.7]

AIM theory takes electron density as a starting point. In this context, the electron density function p represents a three-dimensional function which can be defined as follows p (r) dr is the probability of finding an electron in a small volume element dr at some point in space characterized by the distance r. Bader emphasizes that the electronic density is a real object that can be investigated by computing. [Pg.8]


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See also in sourсe #XX -- [ Pg.154 ]

See also in sourсe #XX -- [ Pg.12 ]

See also in sourсe #XX -- [ Pg.510 ]

See also in sourсe #XX -- [ Pg.462 ]




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