Semiempirical methods population analyses

Many semiempirical methods have been created for modeling organic compounds. These methods correctly predict many aspects of electronic structure, such as aromaticity. Furthermore, these orbital-based methods give additional information about the compounds, such as population analysis. There are also good techniques for including solvation elfects in some semiempirical calculations. Semiempirical methods are discussed further in Chapter 4. 

AIM (atoms in molecules) a population analysis technique AMI (Austin model 1) a semiempirical method... 

NBO (natural bond order) the name of a set of population analysis techniques NDO (neglect of differential overlap) the fundamental assumption behind many semiempirical methods... 

We have learned about the unique ordering of the carbon net charges relative to one another. All methods using Mulliken s population analysis, both ab initio and semiempirical, no matter what basis sets are used to construct the wavefunctions, reproduce the following sequence of inductive effects ... 

If wavefunctions are calculated using semiempirical methods that assume zero overlap between atomic orbitals (AOs) on different atomic centers, then a MuUiken population analysis [84, 85] can be applied to the calculated TD to yield transition monopoles distributed over each atomic center. Such an approach has proven to be effective [82] an advantage being that the interaction between distributed monopoles can be computed considerably faster then that between TDCs. At the same time, the basic topology of the donor-acceptor... 

Atoms in Molecules Electrostatic Potentials Chemical Applications Localized MO SCF Methods Molecular Magnetic Properties Natural Bond Orbital Methods Natural Orbitals Population Analyses for Semiempirical Methods Shape Analysis. 

All the various options influence the result of a population analysis. However, before a final assessment can be made we must address the more basic problem of a category for the population analysis. The most popular analysis is the Mulliken analysis for nonorthogonal AOs and equal partitioning of overlap between the two atoms involved. If the ZDO assumption is maintained for the Fock matrix eigenvalue problem, an orthogonalized AO basis must be considered. In such semiempirical methods the symmetric orthogonalization is most frequently implied. 

Population analysis in semiempirical methods fall into two categories. Methods including overlap in the Fock equations use the Mulliken population analysis. The majority of semiempirical methods uses the ZDO approximation, and the net charges are interpreted on the basis of symmetrically orthog-onalized AOs. It is pointed out that this interpretation is not exactly valid, because of truncation and empirical adjustment. But the corresponding nonsymmetrical orthogonalization is not uniquely defined. Charge models based on semiempirical wave functions play an important role in the calculation of molecular electrostatic potentials for reactivity. 

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