Ionic computational modelling

For a same molecular ratio of aqueous NaY solutions (Y = OH, Cl), experimental data underlines specific effects of nascent OH radicals on transient UV and near-IR electronic configurations. Complex investigations of PHET reactions in the polarization CTTS well of aqueous CT and OH ions are in progress. We should wonder whether a change in the size of ionic radius (OH -1.76 A vs Cl" 2.35 A) or in the separation of the energy levels influence early branchings of ultrafast electronic trajectories. A key point of these studies is that the spectroscopic predictions of computed model-dependent analysis are compared to a direct identification of transient spectral bands, using a cooled Optical Multichannel Analyzer... 

In real-world systems, ranging from atmospheric droplets to flue-gas scrubbers, reactions take place over a wide range of pH, temperature, and ionic strength. Computer modeling incorporating the free radical chemistry of S02 autoxidation needs to be applied to these systems to identify gaps in our knowledge and determine which reactions deserve further study. These models should provide... 

Despite the distinction, which is usually drawn between covalent, ionic, metallic and dispersion interactions, all of these are in fact of the same electromagnetic type. The popular notion that covalent interaction occurs by means of electron exchange between atoms has no physical basis. The common distinction between covalent and ionic contributions to an interaction reflects two different computational models, rather than different types of interaction. 

MgO and NaCl are the best examples of this class of ionic solids, which includes NiO, CoO, CaO, BaO, and LiF (24). The morphologies of these solids are represented in Fig. 1, in which the local geometric structures of low-index (100), (010), and (001) faces on edges and corners are illustrated schematically. The morphologies of the microparticles represented in Fig. 1 have been determined on the basis of results obtained experimentally and with computer modeling techniques. 

One could use the Debye-Hiickel ionic-atmosphere model to study how ions of opposite charges attract each other, (a) Derive the radial distribution of cation ( +) and anion (nj concentration, respectively, around a central positive ion in a dilute aqueous solution of 1 1 electrolyte, (b) Plot these distributions and compare this model with Bjerrum s model ofion association. Comment on the applicability of this model in the study of ion association behavior, (c) Using the data in Table 3.2, compute the cation/anion concentrations at Debye-HUckel reciprocal lengths for NaCl concentrations of lO and 10 mol dm", respectively. Explain the applicability of the expressions derived. (Xu)... 

The last chapter, which is on ionic liquids, describes the continuing evolution that is the result of the development of low-temperature molten salts and the contributions of computer modeling. The description of models of molten sihcates contains much of the original material in the first edition, for the models described there are those still used today. 

Alloys Borates Solid-state Chemistry Carbides Transition Metal Solid-state Chemistry Chalcogenides Solid-state Chemistry Diffraction Methods in Inorganic Chemistry Electronic Structure of Solids Fluorides Solid-state Chemistry Halides Solid-state Chemistry Intercalation Chemistry Ionic Conductors Magnetic Oxides Magnetism of Extended Arrays in Inorganic Solids Nitrides Transition Metal Solid-state Chemistry Noncrystalline Solids Oxide Catalysts in Solid-state Chemistry Oxides Solid-state Chemistry Quasicrystals Semiconductor Interfaces Solids Characterization by Powder Diffraction Solids Computer Modeling Superconductivity Surfaces. 

In the text we hand calculated the speciation of a solution containing 1.00 M HCl and 0.010 M Cd(NO,)2 at 25°C and zero ionic strength. Enter the same information into MINTEQA2 and let the program calculate the speciation. Compare your MINTEQA2 result to the result given in the book. Results may differ because of a different choice of Cd-Cl complexes and/or the use of different stability constants for the complexes in the computer model (listed in the file thermo.dbs). Tabulate and compare the two sets of stability constants and explain differences between the results. 

The stoichiometric or total ionic strength (/,) is computed ignoring solution ion pairs, whereas the effective ionic strength takes ion pairs into account. /, is greater than I,. Why Ion activities (a,) must be the same, whichever ionic strength model is used, so that n, = y,m, = 7/>np where the subscript t denotes total ion values that apply when /, is used. Subscript/indicates free ion values should be used when is employed. Explain and contrast the two approaches with an example. 

The aqueous solubility of a compound is another key property in drug discovery and poor solubility is often the cause of a series demise. Aqueous solubility is inversely related to lipophilicity. High-throughput methods are now available to measure solubility, " but approaches to estimate solubility from computational models are less suc-cessfnl. The models are not sufficiently accurate to predict poor solubility with great precision. Moreover, solubility is influenced by many factors such as ionic strength, type of buffer, crystal packing, etc., all properties which are difficult... 

The validity of the simple ionic bond model is supported by the fact that not only the observed static structures of the clusters are in rather good agreement with the computed stable configurations, but that the dynamic behavior of the clusters is also described by the model. 46)... 

Using a computer model developed from solution equilibrium techniques discussed by Lindsay [4], analytical data were used to calculate the activities and molarities of 29 species in solutions recovered from the coquina columns. A typical computer print-out shown in Figure 1 lists the solution species as well as their activities and molarities. The resulting data were used to interpret the effects of initial pH, ionic strength, acid rain composition and column length on degradation of coquina. 

Steady-state numerical simulations of fluid flow and cupric ion transport within an electrochemical fountain plating system are presented. Specifically, the diffusion-limit is determined directly from the computed flux of cupric ions to the wafer under the assumption of complete surface consumption. This maximum flux, in turn, determines the maximum ionic current that can be passed through the electrolyte to the wafer, which is called the limiting current. The goal of the present study is to predict variations in the limiting current density for different electrolyte volumetric flow rates and wafer (cathode) rotation rates. The efficacy of different computational models, including one-dimensional, two-dimensional axisymmetric, and three-dimensional approximations, are assessed via comparisons of numerical predictions with experimental data. 

Fig. 14. pH gradient, deviation from linearity (A), buffering power (p) and ionic strength (/) of Bier s system of Fig. 13. Their data have been recalculated by using the same molarity and p/f values and the same pH interval as in Fig. 13, except that Tris and cacodylate were assumed to be two Immobilines (i.e., with mobility = 0, flux = 0, diffusion coefficient = 0). Note that the shape of the expected pH gradient is identical in the two different computer models. Our computer simulation predicts that Bier s gradient is fully compatible with a well-functioning lEF system (ideally, however, we prefer to have an average p = 3 mequiv. L pH, so that the concentrations of the two species should be about doubled). (From Righetti and Gianazza, 1985. Reproduced with permission of the publisher.)...

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