Localized molecular orbital model

The localized molecular orbital model (LMO) (39-41) treats the electrons and nuclei separately. The nuclear contribution is identical to eq. [26] with = Z e, the nuclear charge screened by the irmer shell electrons that are assumed to follow the nuclei. The local units for the contribution from the valence elec-... 

Spherical-domain models of three-center bonds in localized-molecular-orbital models of a nonclassical carbonium ion, B4CI4, and TaeClfJ have been described 49,52) a drawing of a spherical-domain model of the methyl lithium tetramer, (LiCH, is shown in Fig. 31. Large, outer circles represent domains of electron-pairs of C—H bonds. Solid circles represent domains of Li+ ions. Shaded circles represent 4-center lithium-lithium-lithium-carbon bonds — i.e., electron-pair domains that touch, simultaneously, three lithium ions and the kernel of a carbon atom. The... 

This conclusion is further strengthened considerably by the theoretical calculation of CBE originally performed by Pearson and Gray (102) and later on somewhat modified by Pearson and Mawby (8). Values of CBE are calculated according to three models, viz. the hard sphere model, the polarizable ion model and the localized molecular orbital model. Only the last one, treating the bonds as covalent, is able to account in a satisfactory way for the values found experimentally for such halides as HgCl2 and CdCl2. For LiCl and NaCl, on the other hand, an acceptable fit with the experimental values is obtained already by the hard sphere model, which certainly indicates a predominantly electrostatic interaction. 

Nafie LA, Walnut TH (1977) Vibrational circular-dichroism theory - localized molecular-orbital model. Chem Phys Lett 49 441 146... 

L. A. Nafie and T. H. Walnut, Chem. Phys. Lett., 49, 441 (1977). Vibrarional Circular Dichroism Theory A Localized Molecular Orbital Model. T. H. Walnut and L. A. Nafie, ]. Chem. Phys., 67, 1491 (1977). Infrared Absorption and the Born-Oppenheimer Approximation. I. Vibrational Intensity Expression. T. H. Walnut and L. A. Nafie, J. Chem. Phys., 67, 1501 (1977). Infrared Absorption and the Born-Oppenheimer Approximation. II. Vibrational Circular Dichroism. 

The molecular orbital model developed in this section is more elaborate than the localized bonds described earlier in this chapter. Is this more complicated model necessary to give a thorough picture of chemical bonding Experimental evidence for molecular oxygen suggests that the answer is yes. 

Scheme la shows the approximate molecular orbital model for the hypervalent X-E-X 3c-4e in EX4, such as SC14. Characters of the three molecular orbitals are bonding (v /i), nonbonding (v /2), and anti-bonding (v /3). Two electrons are in and two in v 2. Electrons in v 2 localize on X of X-E-X and the hypervalent bonds are mainly characterized by v 2. Consequently,... 

The truncation procedure for fiill-valence-space and N-electrons-in-N-orbitals SDTQ MCSCF waveflmctions is based on choosing split-localized molecular orbitals as configuration generators since they lead to the greatest number of deadwood configurations that can be deleted. A quite accurate estimation method of identifying the latter has been developed so that the truncation can be performed a priori. The method has been shown to be effective in applications to the molecules HNO, OCO and NCCN where, for instance, the energies of the full SDTQ[N/N] calculations are recovered to better than 1 mh by truncated expansions that require only 11.8%, 10.9% and 6.3%, respectively, of the number of determinants in the full calculations. Similar trends are observed for the FORS 1 model. 

Rotational and Dipole Strength Calculations for the CH-Stretching Vibrations of L-alanine Using the Localized Molecular Orbital, Nonlocalized Molecular Orbital, Atomic Polar Tensor, and Fixed Partial Charge Models ... 

A localized molecular orbital representation is the closest approach that can be achieved, for a given determinantal wavefunction, to an electrostatic model of a molecule 44>. With truly exclusive orbitals, electron domains interact with each other through purely classical Coulombic forces and the wavefunction reduces, for all values of the electronic coordinates, to a single term, a simple Hartree product. 

A striking analogy exists between localized molecular orbital, electron-domain models of organic and other covalently bonded molecules (Figs. 3—8) and ion-packing models of inorganic compounds 47). 

It would appear that localized molecular orbital, electron-domain models will prove useful in interpretative studies of the structural chemistry of electron-pair donor-acceptor interactions. 

The localized molecular orbital (LMO) model was first proposed by Nafie and Walnut (1977). In the context of this model the rotatory strength of a vibrational transition is evaluated by seperate contributions of each orbital and each nucleus. 

Unlike [CpMo(CO)2]2 in which unsaturation generates localized metal-metal multiple bonding, here the unsaturation is spread out over the entire six-atom cluster system a conclusion supported by the difference in geometric parameters between the Cr and Re compounds as well as by molecular orbital modeling. Because of the invariant stoichiometry, these observed geometry changes can only be attributed to the change in metal. 

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