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Calculation models

Model calculations usually divide the reaction into two parts and make various assumptions about the nature of the entrance channel (or reactant) and exit channel (or product) interactions. In some models, these interactions are treated independently and in others some degree of coupling is introduced. Not all reaction models are capable of describing the nature of the product energy disposal many are concerned only with the total reaction cross section or the product angular scattering distributions. [Pg.380]

One of the simplest models for describing direct reactions of an atom and a molecule in which the reaction products are scattered in a forward direction with respect to the reagent atom is the spectator-stripping model [167]. This has been satisfactorily applied to many ion—molecule [Pg.380]

A widely-used model in this class is the direct-interaction with product repulsion (DIPR) model [173—175], which assumes that a generalised force produces a known total impulse between B and C. The final translational energy of the products is determined by the initial orientation of BC, the repulsive energy released into BC and the form of the repulsive force as the products separate. This latter can be obtained from experiment or may be assumed to take some simple form such as an exponential decay with distance. Another method is to calculate this distribution from the quasi-diatomic reflection approximation often used for photodissociation [176]. This is called the DIPR—DIP model ( distributed as in photodissociation ) and has given good agreement for the product translational and rotational energy distributions from the reactions of alkali atoms with methyl iodide. [Pg.381]

Truhlar and Dixon [168] have recently presented a comprehensive review of model calculations for direct chemical reactions. [Pg.381]

Cutting across the domains of the various techniques mentioned above, are the model calculations l These are theoretical attempts to predict the structure of surfaces from first principles. The model calculations differ from the theories mentioned in conjunction with the experimental techniques listed above, in that the former are not primarily designed to describe the interaction of a probe with a surface, although obviously much overlap exists. Thus the calculation of electronic states at surfaces seeks to describe from first principles a situation (the structure of the surface) that is analyzed experimentally by any of the techniques mentioned above, using external probes but some of these techniques also involve the motion of electrons througli the surface region this motion in turn is clearly related to the electronic structure of the surface, and so the first-principles calculation and the surface-analysis technique may have and often do have much in common. [Pg.47]


Gallagher Feeder S M and Jonas D 1999 Two-dimensional electronic correlation and relaxation spectra theory and model calculations J. Phys. Chem. A 102 10 489-505... [Pg.280]

U, and model calculations suggest that nonnally has values in the neighbourhood of 1 eV (10 J moD ) for the simplest redox processes. [Pg.605]

Figure A3.6.5. Photoisomerization rate constant of (ran.s -stilbene m n-pentane versus inverse of the self-diflfrision coefficient. Points represent experimental data, the dashed curve is a model calculation based on an... Figure A3.6.5. Photoisomerization rate constant of (ran.s -stilbene m n-pentane versus inverse of the self-diflfrision coefficient. Points represent experimental data, the dashed curve is a model calculation based on an...
Figure C2.17.13. A model calculation of the optical absorjDtion of gold nanocrystals. The fonnalism outlined in the text is used to calculate the absorjDtion cross section of bulk gold (solid curve) and of gold nanoparticles of 3 mn (long dashes), 2 mn (short dashes) and 1 mn (dots) radius. The bulk dielectric properties are obtained from a cubic spline fit to the data of [237]. The small blue shift and substantial broadening which result from the mean free path limitation are... Figure C2.17.13. A model calculation of the optical absorjDtion of gold nanocrystals. The fonnalism outlined in the text is used to calculate the absorjDtion cross section of bulk gold (solid curve) and of gold nanoparticles of 3 mn (long dashes), 2 mn (short dashes) and 1 mn (dots) radius. The bulk dielectric properties are obtained from a cubic spline fit to the data of [237]. The small blue shift and substantial broadening which result from the mean free path limitation are...
SpartanView displays calculated vibrations and frequencies for selected models Calculated frequencies are listed m wavenumbers (cm ) and are consistently larger than observed frequencies (observed frequency = 0 9 X calculated frequency is a good rule of thumb)... [Pg.1266]

The algorithms of the mixed classical-quantum model used in HyperChem are different for semi-empirical and ab mi/io methods. The semi-empirical methods in HyperChem treat boundary atoms (atoms that are used to terminate a subset quantum mechanical region inside a single molecule) as specially parameterized pseudofluorine atoms. However, HyperChem will not carry on mixed model calculations, using ab initio quantum mechanical methods, if there are any boundary atoms in the molecular system. Thus, if you would like to compute a wavefunction for only a portion of a molecular system using ab initio methods, you must select single or multiple isolated molecules as your selected quantum mechanical region, without any boundary atoms. [Pg.108]

Meridional circulation in two-dimensional stratospheric models has been specified based on observations or general circulation model calculations recendy efforts have been undertaken to calculate circulations from first principles, within the stratospheric models themselves. An important limitation of using models in which circulations are specified is that these caimot be used to study the feedbacks of changing atmospheric composition and temperature on transport, factors which may be important as atmospheric composition is increasingly perturbed. [Pg.386]

Based on an average tray efficiency of 90 percent for the hydrocarbons, the eqiiilibniim-based model calculations were made with 36 equilibrium stages. The results for the distillate and bottoms compositions, which were very close to those computed by the rate-based method, were a distillate with 0.018 mol % ethylbenzene and less than 0.0006 mol % styrene, and a bottoms product with only a trace of methanol and 0.006 mol % toluene. [Pg.1292]

LG Boulu, GM Crippen. Voronoi binding site models Calculation of binding models and influence of drag binding data accuracy. I Comput Chem 10(5) 673-682, 1989. [Pg.367]

A calculation of tunneling splitting in formic acid dimer has been undertaken by Makri and Miller [1989] for a model two-dimensional polynomial potential with antisymmetric coupling. The semiclassical approximation exploiting a version of the sudden approximation has given A = 0.9cm" while the numerically exact result is 1.8cm" Since this comparison was the main goal pursued by this model calculation, the asymmetry caused by the crystalline environment has not been taken into account. [Pg.104]

Molecular modelling calculations using values of smaller than 3 Angstrom units for these proton-proton distances can be performed to obtain an optimized picture of the molecule. But this exceeds the scope of this book. [Pg.249]

The simplest diffraction measurement is the determination of the surface or overlayer unit mesh size and shape. This can be performed by inspection of the diffraction pattern at any energy of the incident beam (see Figure 4). The determination is simplest if the electron beam is incident normal to the surface, because the symmetry of the pattern is then preserved. The diffraction pattern determines only the size and shape of the unit mesh. The positions of atoms in the surface cannot be determined from visual inspection of the diffraction pattern, but must be obtained from an analysis of the intensities of the diffracted beams. Generally, the intensity in a diffracted beam is measured as a fimction of the incident-beam energy at several diffraction geometries. These intensity-versus-energy curves are then compared to model calculations. ... [Pg.259]

Surface atomic structure. The integrated intensity of several diffracted beams is measured as a fimction of electron beam energy for different angles of incidence. The measurements are fitted with a model calculation that includes multiple scattering. The atomic coordinates of the surfiice atoms are extracted. (See also the article on EXAFS.)... [Pg.260]

The Raman and infrared spectra for C70 are much more complicated than for Cfio because of the lower symmetry and the large number of Raman-active modes (53) and infrared active modes (31) out of a total of 122 possible vibrational mode frequencies. Nevertheless, well-resolved infrared spectra [88, 103] and Raman spectra have been observed [95, 103, 104]. Using polarization studies and a force constant model calculation [103, 105], an attempt has been made to assign mode symmetries to all the intramolecular modes. Making use of a force constant model based on Ceo and a small perturbation to account for the weakening of the force constants for the belt atoms around the equator, reasonable consistency between the model calculation and the experimentally determined lattice modes [103, 105] has been achieved. [Pg.55]

The simple terrain estimate is adjusted to represent a 24-hour average by multiplying by a factor of 0.4, while the VALLEY 24-hour estimate incorporates the 0.25 factor used in the VALLEY model. Calculations continue for each terrain height/distance combination entered until a terrain... [Pg.303]

The SCREEN model calculates plume rise for flares based on an effective buoyancy flux parameter. An ambient temperature of 293° K is assumed in this calculation and therefore none is input by the user. It is assumed that 55 percent of the total heat is lost due to radiation. [Pg.309]

Table 1. Comparison of experimentally observed electronic shell closings with model calculations ... Table 1. Comparison of experimentally observed electronic shell closings with model calculations ...
Use of the term mean-bulk temperature is to define the model from which temperatures are computed. In shock-compression modeling, especially in porous solids, temperatures computed are model dependent and are without definition unless specification of assumptions used in the calculations is given. The term mean-bulk temperature describes a model calculation in which the compressional energy is uniformly distributed throughout the sample without an attempt to specify local effects. In the energy localization case, it is well known that the computed temperatures can vary by an order of magnitude depending on the assumptions used in the calculation. [Pg.151]

Waclii, S. and Jones, A.G., 1990. Model calculations of precipitation with gas-liquid rapid chemical reaction. In Industrial Crystallization 90. GaiTnisch-Partenkirchen, September 1990. Ed. A. Mersmann, Diisseldorf GVC.VDI, pp. 229-235. [Pg.326]

Fig. 7. Model calculations for the reflectivity (a) and the optical conductivity (b) for a simple (bulk) Drude metal and an effective medium of small metallic spherical particles in a dielectric host within the MG approach. The (bulk) Drude and the metallic particles are defined by the same parameters set the plasma frequency = 2 eV, the scattering rate hr = 0.2 eV. A filling factor/ = 0.5 and a dielectric host-medium represented by a Lorentz harmonic oscillator with mode strength fttOy, 1 = 10 eV, damping ftF] = I eV and resonance frequency h(H = 15 eV were considered for the calculations. Fig. 7. Model calculations for the reflectivity (a) and the optical conductivity (b) for a simple (bulk) Drude metal and an effective medium of small metallic spherical particles in a dielectric host within the MG approach. The (bulk) Drude and the metallic particles are defined by the same parameters set the plasma frequency = 2 eV, the scattering rate hr = 0.2 eV. A filling factor/ = 0.5 and a dielectric host-medium represented by a Lorentz harmonic oscillator with mode strength fttOy, 1 = 10 eV, damping ftF] = I eV and resonance frequency h(H = 15 eV were considered for the calculations.
The main phenomenological difference in BM compared to MG is a broadening of the resonance peak at which, however, does not shift. The model calculations in Fig. 11 have been performed for spheres (N = 1/3) with filling factors of 0.5 and 0.9. The parameters, chosen to be equal for both models, are given in the figure caption. It immediately appears that we will not find any drastic difference in the interpretation of the data for the MG or the BM model. [Pg.101]

What is striking in our model calculations is the rather good agreement of the (Up and r parameters for oqi between our optical (in the MG model) and the ESR results [7]. In fact, the ESR scattering time tESR jq-13 along the quasi onedimensional CNTs implies a a c of 10 S/cm for an [7], which is in agreement with a c = /r = 1700 S/cm evaluated from the optical parameters (Table... [Pg.103]

In a recent paper [11] this approach has been generalized to deal with reactions at surfaces, notably dissociation of molecules. A lattice gas model is employed for homonuclear molecules with both atoms and molecules present on the surface, also accounting for lateral interactions between all species. In a series of model calculations equilibrium properties, such as heats of adsorption, are discussed, and the role of dissociation disequilibrium on the time evolution of an adsorbate during temperature-programmed desorption is examined. This approach is adaptable to more complicated systems, provided the individual species remain in local equilibrium, allowing of course for dissociation and reaction disequilibria. [Pg.443]


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Angular overlap model calculations

Approximate Calculations and Models

Assumptions made in the calculation of model ages

Austin Model 1 structure calculation

Batch Fractional Distillation Model Equations and Some Simple Algebraic Calculations

Boundary element method model calculations

Box model calculation

Broken bond model calculation

Calculation by Rouse model

Calculation by reptation model

Calculation molecular modelling

Calculation of Conversion by the Dispersion Model

Calculation of Ffor a Simple Model

Calculation of Model Parameters

Calculation of Relative Stability in a Two-Variable Example, the Selkov Model

Calculation of model

Calculation sequence for the simplified turbine model

Calculations with cross-linked network model

Calculations, band theory cluster model

Calculations, oligosaccharide modeling

Calculator, various models

Cluster model calculations

Coal, model calculation

Coal, model calculation combustion systems

Competitive adsorption isotherm, model calculation

Correlated calculations model potential issues

Crevice corrosion calculation model

Diffuse layer model 380 example calculation

Diffusion calculations—reaction models

Energy Calculations Based on Molecular Models

First principles calculations model clusters

Formula weight calculating from molecular models

Free-energy calculations square-well model

Hartree-Fock calculations models

Hat-curved models spectral calculations

Heat model calculation

Hitness models, risk calculation

Hydraulic systems calculation model

Hydrogen atom, calculations Schrodinger model

Illustration of Model Calculations

Independent-particle model, wave function calculations

Induction parameter model calculations

Intake calculation models

Interaction between model calculations

Interaction parameters between model calculations

Intermolecular interaction property based potential model calculations

Kinetic isotope effects model calculation

Lattice model calculations

Linear model, risk calculation

Mathematical modeling example calculations

Metalloproteins, quantum chemical calculations models

Miedema model calculated heats

Model Calculation for the Glass Transition with an Underlying Heating Rate

Model Calculations Related to Underlying Chemistry in PHIP

Model Compounds and Theoretical Calculations

Model age calculation

Model calculations, in the theory

Model calculations, sensitization

Model calculations, thermodynamic

Model core potential calculation

Model for Calculating the Leakage

Model for equilibrium calculations

Model potential calculations

Model reactions, Grignard calculations

Model storage calculation

Model, perturbation calculation and diagrams

Model-calculated evolution

Modeling overview calculations

Modeling solubility NELF model calculations

Modelling and calculations

Modelling calculations, methodology

Modelling/DFT calculations

Models Based on MD Calculations

Models Monte Carlo calculations

Models for Calculation of Surface Area and Pore Sizes

Molecular mechanics calculations, model

Molecular modeling affinity calculation

Molecular modeling calculations

Molecular modeling semiempirical calculations

Molecular modeling spectra calculations

Molecular-level modeling calculations

Monte Carlo calculations behavior, modeling

Multipole contributions potential model calculations

NELF model solubility calculations

Neon model calculation

Numerical Calculations for a Complex Model

Numerical modelling calculations

Ordering models diagram calculations

Particle model, calculation

Particle model, calculation intensity

Particle model, calculation theoretical scattered

Phase model calculations

Point charge model, calculations

Polymer adsorption models in field calculations

Pre-processing for Model Calculation

Predictive modelling calculations

Property based potential model calculations

Qualitative models, electronic structure calculations

Quantum chemical calculation continuum solvation models

Quantum chemical calculation molecular cluster model

Quantum chemical calculations solvation models

Quantum chemical calculations, molecular modeling

Quantum chemical models/calculation

Relativistic Ab-Initio Model Potential Calculations

Relativistic Ab-Initio Model Potential Calculations for Molecules and Embedded Clusters

Results of Model Calculations

Results of Model Calculations for the Cu-Ni System

Sample Calculation with One-velocity Model

Scalar models for calculating aerial image intensity

Screened hydrogenic model calculations

Self-consistent field calculations models

Shell-model calculations

Simultaneous Calculation of Pressure and Chemical Potential in Soft, Off-Lattice Models

Single coordinate model, molecular calculation

Solvation models calculation comparison

Some Model Calculations

Steady state kinetic theory model calculations

Steady state theory model calculations

Stellar model calculations

Strain energies calculational models

Structure calculations model

Subject model calculations

Surface protonation model calculations

The Model for Temperature Calculation

Theories scattering function model calculation

Thermodynamic modeling calculations

Trajectory calculations stochastic model

Two-Zone Model Calculation

Typical Calculations with the Network Junction Model

Using the Macrofluid Model to Calculate Limits of Performance

Vapor-Liquid Phase Equilibrium Calculations with the PVDW Model

WSCC Furnace Model Calculations

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