Atomic charges Mulliken-type analysis

Table 3 Net charges in the carbon atoms in various polyacetylene models obtained by different methods using a Mulliken-type population analysis (in millielectrons)...

Charge Distribution. In Table 7 the net atomic charges on the two carbon atoms (not related by symmetry) and on the hydrogen are shown for all four PDA structures studied. These charges have been calculated again with a Mulliken-type population analysis of HF Bloch functions obtained with an electrostatically balanced (N—16)77 truncation procedure. We found that the charge distributions are also very sensitive to the method of truncation as well as to a proper convergence with respect to N. 

Mulliken-type populations are a useful tool when it comes to analysing the charge and spin distribution in a molecule or solid. However, one must bear in mind that there is rigorously no such thing as an atom in a molecule or in a crystal, and thus such analysis must be viewed somewhat critically. Especially when atomic orbitals are very diffuse, their Mulliken-type populations may not be very realistic. On the other hand, the Mulliken analysis has the advantage that individual atomic orbital occupations may be obtained. 

In semiempirical MO-LCAO calculations of any type, for instance the iterative extended Huckel (lEH) type , the charges on atoms, and more specifically their electronic configurations, are usually calculated by means of a Mulliken population analysis. (Other population analyses may also be efficient). For instance, for the p-electron density on atom A we have ... 

PEF employs partial atomic charges (identical for related atom types) selected from a Mulliken population analysis of a minimal basis set wavefunction computed for a-D-Glcp. Although the relatively low magnitude of these partial atomic charges renders them unsuitable for applications with common models for explicit water, the PEF422 parameters were optimized for modeling isolated carbohydrates, in vacuo, with a dielectric constant (e) of 3 Debye. ... 

Computational methods have been used in order to determine the sulfur chemical speciation on the mineral surface. In one of the first attempt to understand the chalcopyrite surface Von Oertzen et al. have carried out DFT/plane waves calculations on slab models of the (012) and (112) surfaces. Optimization and Mulliken population analyses were performed. After optimization, sulfur polymer chain was observed on (l 12) surface and Mulliken analysis shows a decrease in the charge on the monomeric and polymeric sulfur atoms on the surface, in comparison to the bulk sulfur atom. For the (012) surface, no polymeric chain formation was observed however the monomeric sulfur Mulliken charge on the surface is smaller than those of bulk sulfur atoms. The presence of this three types of sulfur species on the chalcopyrite surface is aligned with Harmer s et al, analyses on XPS spectra. 

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