Natural bond orbital charges

The concept of natural orbitals may be used for distributing electrons into atomic and molecular orbitals, and thereby for deriving atomic charges and molecular bonds. The idea in the Natural Atomic Orbital (NAO) and Natural Bond Orbital (NBO) analysis developed by F. Weinholt and co-workers " is to use the one-electron density matrix for defining the shape of the atomic orbitals in the molecular environment, and derive molecular bonds from electron density between atoms. 

The determination of atomic charges has been a controversial subject because there has been disagreement on how the atoms in a molecule should be defined or, in other words, how the electronic charge should be apportioned between the atoms. Proposed orbital methods for determining atomic charges include the natural bond orbital (NBO) method (Reed et al., 1985, 1988) and the Mulliken method (1985). However, these orbital methods have some unsatisfactory features. There is a certain arbitrary character associated with them because, as we saw in Chapter 3, the choice of orbitals to describe a given molecule is not unique and... 

RHF/3-21G results charges and orbitals were computed utilizing natural bond orbital (NBO)... 

The relative Michael-acceptor abilities of a variety of substituted aromatic and aliphatic nitroalkenes have been elucidated by computational methods. Several global and local reactivity indices were evaluated with the incorporation of the natural charge obtained from natural bond orbital (NBO) analysis. Natural charges at the carbon atom to the NO2 group and the condensed Fukui functions derived by this method were found to be consistent with the reactivity.187... 

Table 7.6 Comparison of Mulliken and natural bond orbital (NBO)/natural population analysis (NPA) charges in LiH and LiF using different basis sets and computational approaches. ...

The tt-overlap populations between both phenyl and amino moieties are in line with a shorter C—N bond distance. Figure 5 gives a summary of the atomic natural charges and bond indices, computed using the natural bond orbital (NBO) approach. The following bond indices, C1-N7 1.11, C1-C2 1.35, C2-C3 1.45 and C3-C4 1.42, indicate that the CN bond is slightly more than a single bond and the CC bonds are less than... 

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