Mulliken charge analysis

Some further refinement can be added to this picture. Mulliken charge analysis has shown15 that gold atoms at kinks and steps have a smaller... 

In addition to Mulliken charge analysis, ADF calculates several atomic charges that do not share the flaws of Mulliken (strong basis set dependence). These charge analysis methods ( Voronoy deformation density and Hirshfeld provide atomic charges that agree well with chemical intuition. 

The band-structure code, called BAND, also uses STO basis sets with STO fit functions or numerical atomic orbitals. Periodicity can be included in one, two, or three dimensions. No geometry optimization is available for band-structure calculations. The wave function can be decomposed into Mulliken, DOS, PDOS, and COOP plots. Form factors and charge analysis may also be generated. 

By default, Gaussian jobs perform a Mulliken population analysis, which partitions the total charge among the atoms in the molecule. Here is the key part of output for formaldehyde ... 

This exercise will examine other ways of computing charges other than Mulliken population analysis. Since atomic charge is not a quantum mechanical observable, all methods for computing it are necessarily arbitrary. We ll explore the relative merits of various schemes for partitioning the electron density among the atoms in a molecular system. 

The Mulliken scheme places the negative charge more or less evenly on the three carbons, and splits the positive charge among the hydrogens. Mulliken population analysis computes charges by dividing orbital overlap evenly between the two atoms involved. 

An example of quantum mechanical schemes is the oldest and most widely used Mulliken population analysis [1], which simply divides the part of the electron density localized between two atoms, the overlap population that identifies a bond, equally between the two atoms of a bond. Alternatively, empirical methods to allocate atomic charges to directly bonded atoms in a reasonable way use appropriate rules which combine the atomic electronegativities with experimental structural information on the bonds linking the atoms of interest. A widely used approach included in many programs is the Gasteiger-Hiickel scheme [1]. 

As an example of Mulliken CT complexation, let us consider the benzene bromine complex, whose optimized structure and leading intermolecular NBO interaction are displayed in Fig. 5.41. NBO charge analysis of the C6H6- -B complex reveals the presence of slight CT (0.(X)21 e) from C6H6 to Br2, which is consistent with the Mulliken description. Both monomers are altered by complex formation, with the Br—Br bond NBO becoming noticeably polarized away from the benzene ring,... 

Two general techniques are used to extract charges from wave functions - the Mulliken population analysis, based on partitioning the electron distribution, and the ESP method, based on fitting properties which depend on the electron distribution to a model which replaces this distribution by a set of atomic... 

---