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The Approximation

When extending the molecular orbital concept developed for the monoelec-tronic species H2 to polyelectronic diatomic molecules, we start by acknowledging the role of two fundamental approximations (a) one associated with the existence of two nuclei as attractive centres, namely the Born-Oppenheimer approximation, as already encountered in H2 and (b) the other related to the concept of the orbital when two or more electrons are present, that is the neglect of the electron coulomb correlation, as already discussed on going from mono- to polyelectronic atoms. Within the orbital approach, an additional feature when comparing to H2 is the exchange energy directly associated with the Pauli principle. [Pg.114]

The Born-Oppenheimer approximation treats the nuclear motion and the electron motion as entirely independent, which is reasonable in view of the huge difference of mass for nuclei and electrons. This means that the electronic energy is calculated for a given geometric arrangement of the nuclei and the internuclear repulsion is then added as a separate term. [Pg.114]

Just as for polyelectronic atoms, the electronic wavefunction for a molecule must be antisymmetric the Pauli principle. Thus, electron spin correlation is accommodated by the definition of the wavefunction as a Slater determinant whose elements are the occupied molecular orbitals. [Pg.115]

Relativistic corrections are usually neglected and this is acceptable whenever we have elements of not too high an atomic number and providing that we are dealing with valence electrons which have a small probability of being close to the nuclei, as is often the case. [Pg.115]

Since an analytical solution of the Schrodinger equation is no longer possible, the molecular orbitals must be constructed as linear combinations of basis functions using the variation principle. An exact solution would require an infinite set of basis functions, leading to an infinite set of m.o.s. Thus an additional approximation, at the operational level, is introduced which is dependent on the dimension of that set. Further approximations are encountered in the calculation of the m.o.s, depending on the estimation of the various integrals as matrix elements as required by the variation theorem. We shall develop this subject at the end of Chapter 7. [Pg.115]


Because of the approximation given by Equation (22), we obtain a convenient method for determining f for a noncondensable... [Pg.23]

To estimate Henry s constant for solute i in a mixed solvent, we use the approximation... [Pg.56]

The computer subroutine for calculation of liquid-liquid equilibrium separations is described and listed in this Appendix. This is a source routine written in American National Standard FORTRAN (FORTRAN IV), ANSI X3.9-1978, and, as such, should be compatible with most computer systems with FORTRAN IV compilers. The approximate storage requirements for this subroutine are given in Appendix J the execution time is strongly dependent on the separation being calculated but can be estimated (CDC 6400) from the times given for the thermodynamic subroutines it calls (essentially all computation effort is in these thermodynamic subroutines). ... [Pg.333]

Example 4.6 Calculate the process jueld of benzene from toluene and benzene from hydrogen for the approximate phase split in Example 4.2. [Pg.125]

Other techniques such as X-ray diffusion or small angle neutron diffusion are also used in attempts to describe the size and form of asphaltenes in crude oil. It is generally believed that asphaltenes have the approximate form of very flat ellipsoids whose thicknesses are on the order of one nanometer and diameters of several dozen nanometers. [Pg.15]

Accident investigation indicates that there are often many individual causes to an accident, and that a series of incidents occur simultaneously to cause the accident. The following figure is called the safety triangle", and shows the approximate ratios of occurrence of accidents with different severities. This is based on industrial statistics. [Pg.67]

The z-factor must be determined empirically (i.e. by experiment), but this has been done for many hydrocarbon gases, and correlation charts exist for the approximate determination of the z factor at various conditions of pressure and temperature. (Ref. Standing, M.B. and Katz, D.L., Density of natural gases, Trans. AIME, 1942). [Pg.106]

The approximation of Fresnel is scalar approximation. Let u(, r],0-0) be the scalar wave function of the laser beam falling onto the optical element, and u( X,y,Cl) will the be scalar wave function in the plane Z = Cl. Then [3,4]... [Pg.266]

For the determination of the approximated solution of this equation the finite difference method and the finite element method (FEM) can be used. FEM has advantages because of lower requirements to the diseretization. If the material properties within one element are estimated to be constant the last term of the equation becomes zero. Figure 2 shows the principle discretization for the field computation. [Pg.313]

It is worth to mention that the approximation is almost as good in the evaluation area as in the training area. In other words, we seem to have found a regression model with good generalization properties. [Pg.892]

A measurement procedure has been developed that allows to determine the mass of the inclusions as well as their locations with respect to radius, angle, and depth (2). For the depth determination use is made of the approximate 1/R dependence of the magnetic field strength from the distance R to the inclusion When in a first measurement at a small lift off an inclusion is detected, the measurement is repeated at an increased lift off From the signal ratio the depth can be calculated or seen from a diagram like fig. 5a which was generated experimentally. After that, from calibration curves like fig. 5b the absolute value of the signal leads to the mass of the inclusion. [Pg.989]

Table VI-1 shows the approximate values for the Keesom Debye,... Table VI-1 shows the approximate values for the Keesom Debye,...
From the discussion about the Deijaguin approximation for spheres and Eq. VI-26, show that the approximation for two crossed cylinders of radius R is... [Pg.250]

Derive Eq. XIV-11 from Eq. XIV-10. State the approximations involved. Explain whether the surface elasticity should be small or large for a surfactant film if the bulk surfactant concentration is about its CMC. [Pg.527]

We can now calculate the Donnan contribution to film pressure through the use of Eq. III-113 in the approximate form ... [Pg.554]

There is little doubt that, at least with type II isotherms, we can tell the approximate point at which multilayer adsorption sets in. The concept of a two-dimensional phase seems relatively sterile as applied to multilayer adsorption, except insofar as such isotherm equations may be used as empirically convenient, since the thickness of the adsorbed film is not easily allowed to become variable. [Pg.653]

Redhead [89] gives the approximate equation EjRTm - ln(A7) //3)- 3.64. Check the usefulness of this equation by comparing with the answers to Problems 5 and 6. [Pg.740]

Since indistinguishability is a necessary property of exact wavefiinctions, it is reasonable to impose the same constraint on the approximate wavefiinctions ( ) fonned from products of single-particle solutions. Flowever, if two or more of the Xj the product are different, it is necessary to fonn linear combinations if the condition P. i = vj/ is to be met. An additional consequence of indistinguishability is that the h. operators corresponding to identical particles must also be identical and therefore have precisely the same eigenfiinctions. It should be noted that there is nothing mysterious about this perfectly reasonable restriction placed on the mathematical fonn of wavefiinctions. [Pg.26]

It is not possible to solve this equation analytically, and two different calculations based on the linear variational principle are used here to obtain the approximate energy levels for this system. In the first,... [Pg.42]

Nevertheless, equation (A 1.1.145) fonns the basis for the approximate diagonalization procedure provided by perturbation theory. To proceed, the exact ground-state eigenvalue and correspondmg eigenvector are written as the sums... [Pg.48]

For qualitative insight based on perturbation theory, the two lowest order energy eorreetions and the first-order wavefunetion eorreetions are undoubtedly the most usetlil. The first-order energy eorresponds to averaging the eflfeets of the perturbation over the approximate wavefunetion Xq, and ean usually be evaluated without diflfieulty. The sum of aJ, Wd ds preeisely equal to tlie expeetation value of the Hamiltonian over... [Pg.50]

As discussed in section A 1.2.17. the existence of the approximate poly ad numbers, corresponding to short-time bottlenecks to energy flow, could be very important in efforts for laser control, apart from the separate question of bifiircation phenomena. [Pg.78]

L exposure would produce 1 ML of adsorbates if the sticking coefficient were unity. Note that a quantitative calculation of the exposure per surface atom depends on the molecular weight of the gas molecules and on the actual density of surface atoms, but the approximations inlierent in the definition of tire Langmuir are often inconsequential. [Pg.294]

The equilibrium properties of a fluid are related to the correlation fimctions which can also be detemrined experimentally from x-ray and neutron scattering experiments. Exact solutions or approximations to these correlation fiinctions would complete the theory. Exact solutions, however, are usually confined to simple systems in one dimension. We discuss a few of the approximations currently used for 3D fluids. [Pg.478]

The solution detennines c(r) inside the hard core from which g(r) outside this core is obtained via the Omstein-Zemike relation. For hard spheres, the approximation is identical to tire PY approximation. Analytic solutions have been obtained for hard spheres, charged hard spheres, dipolar hard spheres and for particles interacting witli the Yukawa potential. The MS approximation for point charges (charged hard spheres in the limit of zero size) yields the Debye-Fluckel limiting law distribution fiinction. [Pg.480]

The osmotic coefficients from the HNC approximation were calculated from the virial and compressibility equations the discrepancy between ([ly and ((ij is a measure of the accuracy of the approximation. The osmotic coefficients calculated via the energy equation in the MS approximation are comparable in accuracy to the HNC approximation for low valence electrolytes. Figure A2.3.15 shows deviations from the Debye-Htickel limiting law for the energy and osmotic coefficient of a 2-2 RPM electrolyte according to several theories. [Pg.497]

It is important to recognize the approximations made here the electric field is supposed to be sulficiently small so that the equilibrium distribution of velocities of the ions is essentially undisturbed. We are also assuming that the we can use the relaxation approximation, and that the relaxation time r is independent of the ionic concentration and velocity. We shall see below that these approximations break down at higher ionic concentrations a primary reason for this is that ion-ion interactions begin to affect both x and F, as we shall see in more detail below. However, in very dilute solutions, the ion scattering will be dominated by solvent molecules, and in this limiting region A2.4.31 will be an adequate description. [Pg.571]


See other pages where The Approximation is mentioned: [Pg.188]    [Pg.221]    [Pg.889]    [Pg.83]    [Pg.204]    [Pg.233]    [Pg.527]    [Pg.620]    [Pg.621]    [Pg.24]    [Pg.25]    [Pg.36]    [Pg.44]    [Pg.46]    [Pg.75]    [Pg.88]    [Pg.427]    [Pg.457]    [Pg.460]    [Pg.480]    [Pg.484]    [Pg.509]    [Pg.593]    [Pg.606]   


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A Further Approximation The AB Equation

A Second Approximation in the Inner Region

A The Continuum Approximation

Accuracy of the KLI Approximation

An approximate equation for the singlet density

Appendix to chapter 4. The random phase approximation

Applications of the simplified approximation formula

Approximate Equations of the Adiabatic Theory

Approximate Formulations of the Fock Equations

Approximate Representation of the Diabatic Electronic Wavefunction

Approximate Solutions of the PB Equation

Approximate Solutions of the Schrodinger equation

Approximate Treatments of the HJ Ground Electronic State

Approximate forms of the macroscopic rate coefficient

Approximate neglect of pressure variations in the intermediate diffusion range

Approximate solution for the structure of a detonation

Approximate solution of the Dirac equation

Approximate value of the diffusivity

Approximating the Schrodinger Equation

Approximating the saturated vapor pressure of liquids

Approximation by the Use of Difference Equations

Approximation for the Valence Energy

Approximation of the Convective Transport Terms

Approximation of the Diffusive Transport Terms

Approximation of the Effectiveness Factor for Bimolecular Reactions

Approximation of the process impulse response

Approximation of the process transfer function

Approximation of the stress-strain curve

Approximation to the Energy-Transfer Cross-Section

Approximations for the direct correlation function

Approximations that further simplify the energy equation

Approximations to the Coulomb-Breit matrix elements

Approximations to the Many-Electron Wave Function

Approximations to the Poisson-Boltzmann Equation

Approximations towards the Cooper-Zare model

Better Approximate Solutions of the Time-Independent Schrodinger Equation

Beyond the Born-Oppenheimer Approximation

Beyond the Harmonic Approximation

Beyond the Local Density Approximation

Beyond the Orbital Approximation

Beyond the Single-Configuration Approximation

Beyond the adiabatic approximation

Box 6-2 The Logic of Approximations

Breakdown of the Independent Electron Approximation

Breakdown of the Normal Mode Approximation

By Yehuda Haas and Shmuel Zilberg The Crude Born-Oppenheimer Adiabatic Approximation of Molecular Potential Energies

Capillary Forces Calculated with the Circular Approximation

Common Approximations for the Current Distribution

Conductivity imaging by the Born approximation

Correction of the Crude Adiabatic Approximation

Criticism of the Gaussian approximation

Demixtion curves and the Flory-Huggins approximation

Dependent Tunneling in the Born-Oppenheimer Approximation

Developing a long-pipe approximation to the full compressible flow equations

Dois Approximate Solution of the Smoluchowski Equation

Domain Partition and Linear Approximation of the Yield Function

Ellipsoid in the Electrostatics Approximation

Energy bands in the free-electron approximation symmorphic space groups

Equilibrium between an oxide and oxygen the Wagner prevalent defect approximation

Error of the difference approximation

Example using the long-pipe approximation

Exciton states beyond the Heitler London approximation

Expansion and approximation of the Poisson-Boltzmann equation to one non-zero term only

Finite difference approximation of the boundary-value problem

Harmonic approximation of the potential

Helmholtz Free Energy from the CS Approximation

High frequency (WKBJ) approximation for the Greens function

High frequency approximations in the solution of an acoustic wave equation

Horners method for approximating to the real roots of numerical equations

How does the Born-Oppenheimer approximation break down

Integral approximations of the acoustic wavefield

Ion-Solvent Interactions According to the Mean Spherical Approximation

Ionic Fluids in the Mean Spherical Approximation

Linear approximation of the

Local Approximations to the Exact-Decoupling Transformation

Main Approximations of the LSW Approach

Many-Body Perturbation Theory and the GW Approximation

Mechanics of Films The Lubrication Approximation

Methods using a series expansion as an approximation for the exponential integral

Methods using a simple approximation for the exponential integral

Model Hamiltonian in the Kirkwood Approximation

Model Hamiltonians in the Macroscopic Approximation

Molecules and the Born-Oppenheimer Approximation

Moments and the quadrature approximation

Nanosphere in the Quasi-Static Approximation

Nature of the Approximation

Normal modes in the harmonic approximation

Perturbation theory. A comparison with results obtained in the Heitler-London approximation

Physical grounds for the DFT approximations

Polyatomic Systems in Approximation The Cell Model

Possible approximations for the weak base

Properties in the Matrix Approximations

Quantum-mechanical treatment the first Born approximation

Quantum-mechanical treatment the second Born approximation

Quasi-linear approximation of the modified Greens operator

Refinement beyond the simple mean field approximation

Reflectivity under the Kinematic Approximation

Reorientation in the impact approximation

Resolution of the Identity and Local Correlation Approximations

Resolution of the identity approximation

Scattering atmospheres the two-stream approximation

Screening the Thomas-Fermi approximation

Semi-classical Expansion and the WKB Approximation

Some approximation problems in the Hilbert spaces of geophysical data

Some of the worlds most important crop plants and approximate dates for domestication

Spherical approximation of the boundary condition

Successive approximations of the

Symmetry of the One-electron Approximation Hamiltonian

Taylor series approximation of the

The --electron approximation

The AO approximation

The Adiabatic and Born-Oppenheimer Approximations

The Adiabatic and Harmonic Approximations

The Alfrey approximation

The Algebraic Approximation

The Approximate Method

The Atomic-Sphere Approximation (ASA)

The Bar-Graph Approximation

The Basis Set Approximation

The Boltzmann Equation Collision Term Approximation

The Bom-Oppenheimer Approximation

The Born-Oppenheimer Approximation

The Born-Oppenheimer Approximation Potential Energy Surfaces

The Born-Oppenheimer Approximation and its Breakdown Nonadiabatic Processes

The Carnahan-Starling Approximation

The Central Field Approximation (Non-Relativistic)

The Continued Fraction Approximations

The Current Approximation

The Current Approximation Function

The Debye approximation

The Debye-Huckel Approximation Results

The Derjaguin approximation

The Einstein approximation

The Electronic States of Atoms. III. Higher-Order Approximations

The Electrostatics Approximation

The Enskog Approximation

The Finite Difference Approximation

The Fourier Series Approximation

The Franck-Condon Approximation

The Frozen-Core Approximation

The Gaussian approximation

The Generalized Gradient Approximation

The Group Born-Oppenheimer Approximation

The Hard-Rod Approximations

The Harmonic Approximation

The Hartree Approximation

The Hartree-Fock Approximation

The Hartree-Fock approximation in jellium

The Hellmann-Feynman Theorem for Approximate Wavefunctions

The Ideal Gas, Rigid-Rotor Harmonic-Oscillator Approximation

The Independent Electron Approximation

The Inverse Langevin Approximation

The Kirkwood superposition approximation

The LiH molecule approximate molecular orbital calculations

The Line Tension Approximation

The Local Density Approximation

The Long-Chain Approximation

The MARI Approximation

The MO Approximation

The MO-LCAO Approximation

The Mean-Spherical Equal Arm Stretching Approximation General Formalism

The Mean-field Approximation

The Method of Successive Approximations

The Neglect of Differential Overlap Approximation

The No Virtual Pair Approximation

The No-Pair Approximation

The Non-inertial Approximation

The One-Electron Approximation

The One-Valley Approximation

The Orbital Approximation Helium

The Orbital Approximation for Lithium

The PCM-CC-PTE Approximation

The Pairwise Additive Approximation

The Parallel-Series Kinetic Model Approximation

The Pauli Approximation

The Point-Dipole Approximation

The Pool Chemical Approximation

The Pseudo-Steady-State Approximation

The Quasi Steady State Approximation

The Quasi-Equilibrium Approximation Enzymatic Reaction Kinetics

The Quasi-Harmonic Approximation

The Quasi-equilibrium Approximation

The Quest for Approximate Exchange-Correlation Functionals

The Rate-Limiting Step (RLS) Approximation

The Resonant Wave Approximation

The Rigid Rotor Harmonic Oscillator Approximation

The SLG approximation

The Short-Time Approximation

The Singh and Dutt approximation

The Steady-State Approximation

The Stokes approximation

The Thin Film Approximation

The Thin Gap Approximation

The Thin-Gap Approximation - Films with a Free Surface

The Thin-Gap Approximation - Lubrication Problems

The Trapezoidal Approximation

The Two-Centre Approximation

The Valence-Electron Approximation

The Variational Approach to Approximations

The WKB Approximation

The Wavefunctions of Many-Electron Atoms Can Be Described to a Good Approximation Using Atomic Orbitals

The Xa Exchange Approximation

The Z 1 approximation

The Zero-Field Approximation

The approximate integration of differential equations

The approximation of a -pdf

The approximation of a lognormal-pdf

The boundary-layer approximation for laminar flows with chemical reactions

The centroid molecular dynamics approximation

The cluster expansion and super-position approximation

The diagonalized quasi-analytical (DQA) approximation

The dipole approximation

The extended steady-state approximation

The flame sheet approximation

The high temperature approximation

The incoherent approximation

The linear approximation

The molecular field approximation

The nearest-available-neighbour approximation

The nearly free electron approximation

The orbital approximation

The parabolic approximation

The parton model as an impulse approximation

The perturbation is always large in polarization approximation

The pre-equilibrium approximation

The pseudo-binary approximation

The q-Centroid Approximation

The quasi-static approximation

The quasi-steady approximation

The quasi-steady-state approximation (QSSA)

The rate-determining step approximation

The rotating wave approximation

The shortened superposition approximation

The simple current approximation

The simple-tree approximation

The single-particle approximation

The spectator electrons approximation

The steady-state and partial-equilibrium approximations

The steady-state approximation (SSA)

The summarized approximation method

The superposition approximation

The tight binding approximation

The weak acid where both approximations are valid

The weak acid where both approximations can be made

The weak base where both approximations can be made

Tin Orbitals and the Atomic Sphere Approximation

Total Energies in the Local Density Approximation

Tunneling Corrections Based on the Adiabatic Approximation

Two-Electron Terms and the Douglas-Kroll-Hess Approximation

Use of the RLS Approximation

Use of the Steady-State Approximation

Validity of the Approximations

Validity of the BO approximation

Vibrational Properties Beyond the Harmonic Approximation

Within the ZDO approximation

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