Natural bond orbital theory

The natural bond orbital (NBO) method of Weinhold et al. [8, 57] provides a scheme appropriate to the analysis of Lewis acid/base interactions [8, 58] as it emphasizes the calculation of delocalization of electron density into unoccupied orbitals. 

An interesting example is provided by the NBO analysis of the water dimer H20- -HOH, where the left and right molecules behave as the Lewis base and the Lewis acid, respectively. The interaction energy is decomposed into charge transfer (CT) and no charge transfer (NCT) as follows  

The values of the CT term calculated by the NBO scheme are very much larger than those found by most other methods. It should not be concluded that the NBO energy decomposition analysis is wrong in principle. The divergence should rather be attributed to a different operational deflnition of the charge transfer energy. 

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Several schemes for the analysis of the wave function have been proposed. The most commonly used are those proposed by Mulliken and Lbwdin, those based on natural bond orbital theory (NBO), the Bader AIM theory, and the fitting of the electrostatic potential. 

Ab initio electron correlated calculations of the equilibrium geometries, dipole moments, and static dipole polarizabilities were reported for oxadiazoles <1996JPC8752>. The various measures of delocalization in the five-membered heteroaromatic compounds were obtained from MO calculations at the HF/6-31G level and the application of natural bond orbital analysis and natural resonance theory. The hydrogen transfer and aromatic energies of these compounds were also calculated. These were compared to the relative ranking of aromaticity reported by J. P. Bean from a principal component analysis of other measures of aromaticity <1998JOC2497>. 

Because we are both computational chemistry researchers, we have naturally directed the book also to specialists in this field, particularly those wishing to incorporate natural bond orbital (NBO) and natural resonance theory (NRT) analysis into their methodological and conceptual toolbox. Researchers will find here a... 

MRMP multireference Moller—Plesset perturbation (jt-CI) theory (with -configuration interaction) NBO natural bond orbital (analysis)... 

Also in 2-substituted ethanesulphonates,35 the 33S chemical shift has a reverse substituent effect and correlates with both Taft substituent constants and the chemical shift of the carboxylic carbon in related carboxylic acids. It seems that the substituent effect does not depend on conformation, but prevailingly on intramolecular electronic effects. Density functional theory (DFT) calculations of 33S nuclear shielding constants and natural bond orbital (NBO) analysis made it possible to conclude that substituents cause a variation in the polarization of the S-C and S-O bonds and of the oxygen lone pairs of the C — S03 moiety. This affects the electron density in the surroundings of the sulphur nucleus and consequently the expansion or contraction of 3p sulphur orbitals. 

Natural Atomic Orbital and Natural Bond Orbital Analysis 230 9.7 Computational Considerations 232 9.8 Examples 232 References 234 10 Molecular Properties 235 104 Examples 236 References 294 12 Transition State Theory and Statistical Mechanics 296 12.1 Transition State Theory 296 12.2 Statistical Mechanics 298 12.2.1 ans 299 12.2.2 300... 

Decomposition of interaction energies is desired for qualitative chemical analyses of complicated multi-valent interactions in supramolecular aggregates but such a decomposition cannot be uniquely defined within fundamental physical theory. A popular semi-quantitative decomposition method with nice formal features to be mentioned in this context is Weinhold s natural bond orbital (NBO) approach to intermolecular interactions [232, 233]. Comparable is the recently proposed energy decomposition analysis by Mo, Gao and Peyerimhoff [234, 235] which is based on a block-localized wave function. Other energy decomposition schemes proposed are the energy decomposition analysis (EDA) by Kitaura and Morokuma [236] and a similar scheme by Ziegler and Rauk [237]. 

All calculations in Ref. [22] were performed utilizing the Gaussian-98 code [30]. The potential energy scan was performed by means of the Mqller-Plesset perturbation theory up to the fourth order (MP4) in the frozen core approximation. The electronic density distribution was studied within the population analysis scheme based on the natural bond orbitals [31,32], A population analysis was performed for the SCF density and MP4(SDQ) generalized density determined applying the Z-vector concept [33]. 

The model most widely used to explain hypervalence is the three-center, four-electron (3c-4e) model of Rundle and Pimentel [5]. Coulson [31] analyzed the 3c-4e model and suggested a valence bond resonance model that shares some similarities with the MO model. Under this model, the bond is posited to arise primarily from resonance between F-X F and F X -F charge structures (with contributions from other charge configurations). Weinhold and Landis [32] incorporated natural bond orbital analysis and natural resonance theory in what is perhaps the most... 

The EBO concept rehes on a multi-configurational wavefunction and takes into account the effect of electron correlation involving the antibonding orbitals. There are various ways of quantifying bond orders [12-14]. The Natural Bond Orbital (NBO) valence and bonding concepts are also extensively used in the analysis of multiple bonds. NBO, like EBO, is based on a quantum mechanical wavefunction. The NBO description of a bond can be derived by variational, perturbative, or density functional theory (DFT) approximations of arbitrary form and accuracy [15]. 

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