Charge mapping analysis

Baekelandt, B. G., Janssens, G. O. A., Toufar, H., Mortier W. J., Schoonheydt, R. A., and R. F. Nalewajski. 1995. Mapping between electron population and vibrational modes within the charge sensitivity analysis. J. Phys. Chem. 99 9784—9794. 

The Fourier syntheses of various residual density maps based on x-ray and neutron diffraction measurements seem to indicate that present-day diffraction data have sufficient information to pursue quantitative charge density analysis. One route is by a least squares analysis of x-ray data with generalized x-ray-scattering factors. However, published applications of the method do not lend themselves to a critical evaluation of... 

Figure 3.4 Laplacian maps from experimental charge density analysis with (3, -1) critical points (CP) for compounds (a) VCLl, (b) VCL2 and (c) VCL3. The contours are drawn on the logarithmic scale.

Most of the relevant features of the charge density distribution can be elegantly elucidated by means of the topological analysis of the total electron density [43] nevertheless, electron density deformation maps are still a very effective tool in charge density studies. This is especially true for all densities that are not specified via a multipole model and whose topological analysis has to be performed from numerical values on a grid. 

Molecular Probe Analysis. In an effort to understand how a molecule is seen by either another molecule or by a surface, molecular probes can be moved around a chemical to map out its surface. These probes include anions and cations (point charges) and hard spheres or can be constructed as a combination of these. The empirical potential energy is computed at a variety of points around the test molecule and an energy surface is thus generated. This can be examined graphically and compared as changes are made to the molecule. 

The study of the nature of the Si—O bond through analysis of its charge density is based on net ionic charges, heights of peaks in atom deformation density maps, and, more recently, topological analysis of the total charge density. 

After charging, the decay of the open-circuit surface potential is measured. From these measurements, important information can be extracted. In the past few decades, the xerographic probe technique has become a very popular and unique means to characterize electronic gap states. In particular, a map of states near mid-gap is determined by a time-resolved analysis of the xerographic surface potential. 

Analysis of the time and temperature dependent decay of the surface voltage on an amorphous film after charging, but prior to exposure (xerographic dark decay), and of residual decay after exposure can (in combination) be used to map the density of states. 

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