Electronic polarizability studies

FORMALISMS FOR THE EXPLICIT INCLUSION OF ELECTRONIC POLARIZABILITY IN MOLECULAR MODELING AND DYNAMICS STUDIES... 

A new, more accurate electron diffraction study of gaseous mercuric chloride has been reported.159 The interatomic distances (Hg—Cl = 2.25 A, Cl—Cl = 4.48 A) are shorter than previously reported values by 0.02 to 0.09 A. A complete normal-co-ordinate analysis of bis(methylthio)mercury has also been reported.160 The Raman spectra of gaseous mercuric chloride, bromide, and iodide have been reported.161 The bond polarizability derivatives calculated from the data increase in the order Cl < Br < I, suggesting an increased degree of covalence in the mercury-halogen bond with increasing size of the halogen atom. 

The structure of vibration bands of the first and the second order in SWCNT Raman spectra has also been studied for ordered and disordered forms of graphite. This was accomplished by decomposition of the complex spectral bands into constituting components. We found proximity of spectral positions in most of spectral components of the nanotubes and graphite and considerable variation of their intensities. This also demonstrates variation of the electronic polarizabilities and can explain anomalous shifts of the harmonic bands 2vq and 2vd for nanotubes in comparison to corresponding bands of a single crystalline graphite. Narrow width of the low frequency mode Vrbm 160 cm leads to reproduction of the G-band structure in the sum harmonic band Vg+Vrbm" 1750 cm while the complex stmcture of the broad Vp band is remarkably reproduced in the Vq+Vg sum tone. The narrow width of SWCNT s 2vd and 2vg harmonics in the Raman spectra may be related to group synchronism effects [72]. 

Studies of nonlinear optical phenomena in conjugated polymers date back to the earliest studies of the polydiacetylenes [219], The large oscillator strength associated with the p-p transition gives rise to a relatively large linear electronic polarizibility. The early work speculated that because of the implied delocalization of charge in the excited state, conjugated polymers would offer opportunities as NLO materials. 

The amount of broadening experienced by alkali metal ions upon binding to a polymer such as Nafion will depend on several factors including nuclear spin, electric quadrupole moment, stability of the hydrated ion, and electronic polarizability. This last factor relates to the ease with which electric field gradients can be produced by binding to an anionic site. Based on the relative change in linewidth upon going from saturation to low water contents, the ions studied so far are related... 

One application of PI-QTST to PT has been to study a model A-H-A PT solute in a polar solvent [77]. This computational study provided a detailed examination of the specific features of PT, including the competition between proton tunneling and solvent activation, the influence from intramolecular vibrational modulation of the PT barrier, and the role of electronic polarizability of both the solute and the solvent. Changes in the total quantum activation free energy, and hence the reaction probability, due to these different effects were calculated (cf. Fig. 18). By virtue of these studies, it was found that to fully understand the rate of a given PT reaction, one must deal with a number of complex, nonlinear interactions. Examples of such interactions include the nonlinear dependence of the solute dipole on the position of the proton, the coupling of the solute dipole to both the proton coordinate and to other vibrational modes, and the intrinsically nonlinear interactions arising from both solute and solvent polarizability effects. Perhaps the most important conclusion... 

Moreover, the calculation of 7 " can be partitioned into several contributions for studies in vacuo the partition is generally done in terms of electronic and vibrational contributions. Here we consider it convenient to make reference to the in vacuo case, adding a further term, the geometry relaxation contribution, measuring the effects on the electronic polarizability due to the changes in the equilibrium geometry induced by the solvent. 

We note that there has been very recent work devoted to the development of force fields for other types of ionic liquid cations including pyridinium [123] and triazolium [124]. Moreover, an electronically polarizable model has been developed and applied to the simulation of [EMIM][N03] [125]. Results from these studies will be discussed in the next section. 

Lopes PEM, Roux B, MacKereU AD. Molecular modeling and dynamics studies with explicit inclusion of electronic polarizability theory and applications. Theor Chem Aa. 2009 124(l-2) ll-28. http //dx.doi.Org/10.1007/s00214-009-0617-x. 

A case study is the plot of AN versus E shown in Figure 13.1.2. While there is a quite good correspondence for the select solvents (and likely for the nonpolar aliphatic solvents), the other classes are considerably off-line. This behavior may be interpreted in terms of the operation of different solvation mechanisms such as electronic polarizability, dipole density, and/or hydrogen-bonding (HB) ability. For instance, the... 

The application of refractions to the study of structures is based on comparing the experimental values with those calculated on various structural assumptions, of which the most important is additivity (Landolt, 1862) in the first approximation (within ca 10 %), the refraction of a compound is the sum of constant increments of different atoms, ions and bonds. Refractions of some isolated atoms can be measured by the deviation of an atomic beam in an inhomogeneous electric field or by spectroscopic methods. In other cases electronic polarizabilities of free atoms were calculated by ab initio methods. All available experimental and the best of the computed refractions of free atoms are presented in Table 11.5. These values can be used to calculate the energy of van der Waals interactions, magnetic susceptibility, or to establish correlations with atomic and molecular-physical properties. The formation of covalent bonds changes the refractions of isolated atoms and their values transform into the covalent refractions, which are different for isolated molecules and for crystals. Direct measurements of RI of A2 molecules or elemental solids give the most accurate information on the covalent refractions, in other cases the latter have to be calculated from molecular refractions by the additive method. 

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