Property Determination from First Principles

The optimization of the refinery performance for individual crude oil feedstocks requires the development of simulation and prediction models of the individual refinery processes. Such a model is Quann and Jaffe s Structure-Oriented Lumping. Individual hydrocarbon molecules are represented by this model, as vectors of incremental structural features that can describe the composition, reactions and properties of petroleum mixtures. The approach allows for the molecular modeling of all refinery processes. 

Gaylor, V. F. Jones, C. N. Rapid and Comprehensive Cmde Oil Evaluation Without Distillation ,7 rf. Eng. Chem. Prod. Res. andDevelop., 1968, 7(3), 191-8. 

Jaubert, J.-N. Neau, E. Peneloux, A. Fressigne, C. Fuchs, A. Pressure, Volume, and Temperature Calculations on an Indonesian Crude Oil Using Detailed NMR Analysis or a 

Predictive Method To Assess the Properties of the Heavy Fractions , Ind. Eng. Ghent. Res., 1995, 34(2), 640-55. 

Selves, J.-L. Cohn, J.-P. Prediction of Kinematic Viscosity of Crude Oil From Chromatographic Data , F e/, 1997, 76(11), 1005-1011. 

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Salanne, M., Simon, C., Turq, R, and Madden, P.A. (2009) Heat-transport properties of molten fluorides determination from first-principles. J. Fluorine Chem, 130, 38. 

In many atomization processes, physical phenomena involved have not yet been understood to such an extent that mean droplet size could be expressed with equations derived directly from first principles, although some attempts have been made to predict droplet size and velocity distributions in sprays through maximum entropy principle.I252 432] Therefore, the correlations proposed by numerous studies on droplet size distributions are mainly empirical in nature. However, the empirical correlations prove to be a practical way to determine droplet sizes from process parameters and relevant physical properties of liquid and gas involved. In addition, these previous studies have provided insightful information about the effects of process parameters and material properties on droplet sizes. 

It is not possible at present to provide an equation, or set of equations, that allows the prediction from first principles of the membrane permeation rate and solute rejection for a given real separation. Research aimed at providing such a prediction for model systems is under way, although the physical properties of real systems, both the membrane and the solute, are complex. An analogous situation exists for conventional filtration processes. The general membrane equation is an attempt to state the factors which may be important in determining the membrane permeation rate for pressure driven processes. This takes the form ... 

The basic concept of organic chemistry is that of Molecular Structure. It includes the idea that molecules can be regarded as isolated objects, i.e. as separable from their environment, that they possess a structure that determines their physical and chemical properties, and finally that this molecular structure can be adequately described by structural formulae. In terms of physics the notion of structure is directly related to the Bom-Oppenheimer description of molecules. Although Molecular Structure makes no appearance in a quantum treatment of molecules starting from first principles [1, 2] the concept is clearly justified by its overwhelming success in organic chemistry. 

The substance-specific kinetic constants, kx and k2, and partition coefficient Ksw (see Equations 3.1 and 3.2) can be determined in two ways. In theory, kinetic parameters characterizing the uptake of analytes can be estimated using semiempirical correlations employing mass transfer coefficients, physicochemical properties (mainly diffusivities and permeabilities in various media), and hydro-dynamic parameters.38 39 However, because of the complexity of the flow of water around passive sampling devices (usually nonstreamlined objects) during field exposures, it is difficult to estimate uptake parameters from first principles. In most cases, laboratory experiments are needed for the calibration of both equilibrium and kinetic samplers. 

Rather few papers have dealt with the computation of thermodynamic functions from the results of ab initio calculations, but for H2, where the latter are of spectroscopic accuracy, Kosloff, Levine, and Bernstein have computed the thermodynamic properties of Ha, Da, and HD, using the best theoretical results.75 This work represents the first example of an accurate determination of a bulk, macroscopic property from first principles. 

Somewhat closer to the designation of a microscopic model are those diffusion theories which model the transport processes by stochastic rate equations. In the most simple of these models an unique transition rate of penetrant molecules between smaller cells of the same energy is determined as function of gross thermodynamic properties and molecular structure characteristics of the penetrant polymer system. Unfortunately, until now the diffusion models developed on this basis also require a number of adjustable parameters without precise physical meaning. Moreover, the problem of these later models is that in order to predict the absolute value of the diffusion coefficient at least a most probable average length of the elementary diffusion jump must be known. But in the framework of this type of microscopic model, it is not possible to determine this parameter from first principles . 

In the context of this book, structure solution from first principles (also referred to as the ab initio structure determination) means that all crystallographic data, including lattice parameters and symmetry, and the distribution of atoms in the unit cell, are inferred from the analysis of the scattered intensity as a function of Bragg angle, collected during a powder diffraction experiment. Additional information, such as the gravimetric density of a material, its chemical composition, basic physical and chemical properties, may be used as well, when available. 

The optical properties of materials are determined by the so-called dielectric function. This dielectric function for para-phenyl-type molecules was determined by first-principles band-structure calculations on PPP.14 In Fig. 8.3, we depict one of the main results, namely the dependence of the imaginary part of the dielectric function (which is proportional to the optical absorption coefficient) on the orientation parallel (ec) and perpendicular (ea, ch) to the chain axis. From a comparison to the experiment, one can see that the optical absorption in the visible and ultraviolet ranges is mainly determined by the dielectric function parallel to the polymer chain. This is shown in Fig. 8.4, where the calculated absorption coefficient of para-hexaphenyl perpendicular to the chains is compared to the experimentally determined absorption perpendicular and parallel to the chains. 

The reactivity of molecules represents their ability to undergo certain interactions. In the extrathermodynamic approach, the reactivity characteristics of molecules are described as changes in the reactivity of a reference molecule upon substitution. It is known from chemistry, however, that molecular interactions are determined by properties of the entire molecule. Quantum chemistry offers the means of obtaining molecular properties from first principles of physics and chemistry the quantum chemical computation methods are now able to predict good relative values of physicochemical properties that can be determined by experiment either with great difficulty or only by inference. 

With the development of current theories of electronic structure, such as multireference ab initio approaches and in particular density-functional theory (DFT), the appealing ligand-field approach became displaced by these approaches theoretically well justified but chemically less transparent and less readily analyzed and interpreted (but see Ref [3] as an exception). In contrast, the parametric strucmre of ligand-field theory and the need of experimental data to allow adjustment of these parameters makes this model a tool for interpretation rather than for predictions of electronic properties of transition-metal complexes. A proposed DFT-supported ligand-field theory (LFDFT) enables one to base the determination of LF parameters solely on DFT calculations from first principle [3-6]. This approach is equally suitable to predict electronic transitions [4] and, with appropriate account of spin-orbit coupling [5], one is able to calculate with satisfactory accuracy g- and A-tensor parameters [6]. 

Adsorption occurs when an incident atom or molecule sticks to the surface. The adsorbing species can be bound weakly to the surface or it can be held tightly to the surface. The manner by which the adsorbed species is held and the properties it exhibits once adsorbed determine the type of adsorption — physical or chemical. The dynamics of the process by which the incident adsorbate finds the adsorption site is used to construct a rate expression and rate constant for the adsorption step from first principles. 

The use of a fractionation technique coupled with the determination of the metal or non-metal content could provide some information about the species under study. This information may include the approximate molecular mass, isoelectric point and electrophoretic mobility. If well-characterised standards are available with similar properties as the species of interest, identification is possible. In practice, however, because of the very limited number of well-characterised standards complete characterisation and identification Is only possible from first principles. Indeed, complete characterisation may not. in some cases, be necessary for the interpretation of the experimental results. Partial characterisation may be all that is needed. Some of the information that may be required and the techniques used are summarised in Table 2. A detailed account of some of the approaches used for structure elucidation and the study of the reactivity of various trace element containing biological molecules can be found in the book by Hughes (1981). 

There are two important points to emphasize with regard to Flf- First, contributions to Flf are not computed from first principles. Instead, the potential is constructed parametrically and the parameter values are determined by fitting calculated properties to experiment. Secondly, there are two distinct ways in which Flf can be constructed-globally or via ligand superposition. 

Transference numbers have formed one of the cornerstones in our understanding of electrolyte solutions. Hittorf s discovery in 1853 that transference numbers depended on the ion, the co-ion, and the solvent proved that each ion in a given solvent possesses its own individual mobility. Even today ionic mobilities must be determined by a combination of transference and conductance experiments for we still cannot predict their values accurately from first principles The importance of ionic mobilities can hardly be overemphasized since they are the only properties of individual ions that can be unambiguously measured (either directly or via trace diffusion coefficients). They therefore provide unique insight into ion-solvent interactions. Hittorf s later transference experiments also revealed the existence and composition of a variety of complex ions in solution. His approach has been followed in more recent structural investigations, for instance in studying the complex ions present in aluminium plating solutions (7A,). 

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