Intramolecular charge distribution

Intramolecular charge distribution depends on the number of valence electrons and electronegativity differences. In some extreme cases it resembles the interactions, traditionally considered to define van der Waals, metallic, ionic or covalent bonding. The true interaction in all cases however, contains elements of all four extremes. 

For molecular van der Waals crystals of non-polar molecules, surface dipoles and work function anisotropy have only recently been explored [5], While variations of several tenths of an eV in the ionization energy (IE the molecular analog to a metal s <(>) depending on the molecular orientation on a surface have been reported several times [6-8], a consistent picture was lacking. An explanation for the intriguing observation that one and the same molecule can have different - still well-defined - IEs in ordered thin films is that the electrostatic potential above a molecular crystal surface is determined by the orientation of the molecules and their intramolecular charge distribution. 

In order to understand ionic distributions in the EDL a realistic description of hydration or, more generally, solvation phenomena is necessary, which in protic liquids implies an adequate description of the hydrogen-bond network. Theory and computer simulation of bulk liquids showed that the most efficient way to include these properties into the models is via distributed charge models in which the intramolecular charge distribution is represented by several point charges. The point charges are adjusted to reproduce experimental dipole and/or quadrupole moments of the molecule, the bulk structure... 

So far we have seen that the APT representation of infrared absorption intensities offers a mathematically efficient way of reducing the experimental data to quantities associated with motions of individual atoms in molecules. In general terms such a rationalization of intensity data appears acceptable since intramolecular charge distribution may be approximately expressed in teims of partial atomic charges provided, of course, that an effective way is found to relate the charge distribution with atomic polar tensors. 

The dispersive force arises due to the intermolecular electron correlation between the solute and the solvent. Further, it is also important to include the changes in intramolecular and intermolecular solvent electron correlation upon insertion of the solute in the solvent continuum. Further, electron correlation affects the structure of the solute and its charge distribution. Hence, the wave function obtained from the calculation with electron correlation provides a more accurate description of reaction field. 

The non-classical-classical debate centres on the question of the relative energy of various structures of the ion. This energy must reflect the bond lengths, angles, charge distributions and intramolecular interactions present in the stmcture. Before proceeding further, it is advisable to consider the major characteristics of the classical and non-classical stmctures of the norbomyl ion. 

The theorem has the important implication that intramolecular interactions can be calculated by the methods of classical electrostatics if the electronic wave function (or charge distribution) is correctly known. The one instance where it can be applied immediately is in the calculation of cohesive energies in ionic crystals. Taking NaCl as an example, the assumed complete ionization that defines a (Na+Cl-) crystal, also defines the charge distribution and the correct cohesive energy is calculated directly by the Madelung procedure. 

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