Mutual polarization

Many problems in force field investigations arise from the calculation of Coulomb interactions with fixed charges, thereby neglecting possible mutual polarization. With that obvious drawback in mind, Ulrich Sternberg developed the COSMOS (Computer Simulation of Molecular Structures) force field [30], which extends a classical molecular mechanics force field by serai-empirical charge calculation based on bond polarization theory [31, 32]. This approach has the advantage that the atomic charges depend on the three-dimensional structure of the molecule. Parts of the functional form of COSMOS were taken from the PIMM force field of Lindner et al., which combines self-consistent field theory for r-orbitals ( nr-SCF) with molecular mechanics [33, 34]. 

The interaction density in water dimer has been the object of previous studies [39,40], In particular, Krijn and Feil[40] pointed out the effects of exchange repulsion and of the dominant mutual polarization of the two moieties arising from the electric fields... 

A smaller repulsion between the reactants due to their mutual polarization. ... 

An alternative formulation of the Fukui functions based on the mutual polarization of the reagents can be constructed as follows [24,32]. In a chemical reaction, the description of a local electron transfer does not need to involve any actual change... 

The Bom equation does not take into account the mutually polarizing effect that the solute and solvent have upon each other. This can be done, within the framework of continuum solvent... 

In contrast to those noted above, theoretical investigations of branched complexes in which two or more hydrogen bonds are formed by one proton-acceptor group, as in Structure 2.4, predict an inverse effect. In this case, mutual polarization weakens the hydrogen bonds, leading to anticooperative effects. The various factors governing the influence of the first hydrogen bond on the formation of... 

Hydrogen bonds can be cooperative or anticooperative based on their mutual polarization. 

One of the important aspect of the use of dihydrogen bonds as driving forces in molecular associations is their cooperativity or anticooperativity when increasing the number of H- H contacts in the self-association of molecular systems leads to additional energy, calculated on the basis of one dihydrogen bond, or vice versa. As we have shown in Chapter 2, classical hydrogen bonds can be highly cooperative, due to their mutual polarization [5]. 

Degrees of Polarity and Mutual Polarization of Ions in the Molecules of Alkali Fluorides, SrO, and BaO... 

A precise quantitative theory of the mutual polarization of ions in molecules is not possible as long as one cannot take into account the inhomogeneity of the field of the polarizing ion and the dependence of the polarizability of the polarized ion on its surroundings. It is therefore attempted to correlate the observed dependence of the p values on r and the polarizability of the ions in a semi-quantitative and semi-empirical fashion. This proves to be successful for the alkali fluorides but explains only qualitatively why the degree of polarity is smaller for BaO than for SrO. 

We arrive at the conclusion that although a precise quantitative theory of the mutual polarization of ions cannot be reached without taking appropriately into account the inhomogeneity of the jrolarizing field and the variability of the polarizabUity of the ions, the discussion in this Sec. 2.3 clarifies semi-quantitatively the factors responsible for the gradation of the degrees of polarity of the alkali fluoride molecules. 

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