Non-binding orbitals

Fig. 20. Schematic representation of the s, p, d and f partial contributions to the total energy of electrons in the conduction band of a light actinide metal. The different R s denote the radial extension of the different contributing orbitals. R (f-included) and R 2n-f refer to the equilibrium volumes when the 5 f electrons are itinerant and when they are non-binding (from Ref. 77)...

Within density-functional theory, a linear combination of overlapping non-orthogonal orbitals from first principles may be utilized to arrive at at full-potential local orbital (FPLO) method [213], and this k-dependent LCAO approach comes close to full-potential APW-based methods (see Sections 2.15.3 and 2.15.4) in terms of numerical accuracy, although FPLO is much faster simply because of the locality of the basis set. Even faster, due to a strongly simplified potential, is a parameter-free (density-functional) tight-binding method called TB-LMTO-ASA, derived through localization of a delocalized basis set (see Section 2.15.4). 

Some of the earliest DNMR observed for organometallics involved the planar rotation of olefins. This process effectively involves a rotation about an axis from the metal to the midpoint of an -alkene and is sometimes called a propeller rotation. In unsymmetrical metal complexes, there is the possibility of several conformers based on orientations of the olefin. This can generally be attributed to differing donor properties of non-equivalent other ligands. The faces of many substituted olefins are enantiotopic, and binding to the metal produces... 

Resonance such as (5.28a)-(5.28c) is inherently a quantal phenomenon, with no classical counterpart. In NBO language, each of the resonance interactions (5.28a)-(5.28c) corresponds to a donor-acceptor interaction between a nominally filled (donor Lewis-type) and unfilled (acceptor non-Lewis-type) orbital, the orbital counterpart of G. N. Lewis s general acid-base concept. As mentioned above, Lewis and Werner (among others) had well recognized the presence of such valence-like forces in the dative or coordinative binding of free molecular species. Thus, the advent of quantum mechanics and Pauling s resonance theory served to secure and justify chemical concepts that had previously been established on the basis of compelling chemical evidence. 

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