Applications of Electronic Structure Theory (Modern Theoretical Chemistry, Volume 4)

These two volumes deal with the quantum theory of the electronic structure of ab initio is the notion that approximate solutions molecules. Implicit in the term of Schrodinger's equation are sought "from the beginning," i. e. , without recourse to experimental data. From a more pragmatic viewpoint, the distin­ guishing feature of ab initio theory is usually the fact that no approximations are involved in the evaluation of the required molecular integrals. Consistent with current activity in the field, the first of these two volumes contains chapters dealing with methods per se, while the second concerns the application of these methods to problems of chemical interest. In a sense, the motivation for these volumes has been the spectacular recent success of ab initio theory in resolving important chemical questions. However, these applications have only become possible through the less visible but equally important efforts of those developing new theoretical and computational methods and models. Henry F. Schaefer vii Contents Contents of Volume 3 xv Chapter 1. A Priori Geometry Predictions 1. A. Pople 1. Introduction . . . . . . . . . . . . . . . . . . . 1 2. Equilibrium Geometries by Hartree-Fock Theory 2 2. 1. Restricted and Unrestricted Hartree-Fock Theories 2 2. 2. Basis Sets for Hartree-Fock Studies . . . . . 4 2. 3. Hartree-Fock Structures for Small Molecules . 6 2. 4. Hartree-Fock Structures for Larger Molecules 12 3. Equilibrium Geometries with Correlation . . 18 4. Predictive Structures for Radicals and Cations 20 5. Conclusions 23 References 24 Chapter 2. Barriers to Rotation and Inversion Philip W. Payne and Leland C.

1. A Priori Geometry Predictions.- 1. Introduction.- 2. Equilibrium Geometries by Hartree-Fock Theory.- 2.1. Restricted and Unrestricted Hartree-Fock Theories.- 2.2. Basis Sets for Hartree-Fock Studies.- 2.3. Hartree-Fock Structures for Small Molecules.- 2.4. Hartree-Fock Structures for Larger Molecules.- 3. Equilibrium Geometries with Correlation.- 4. Predictive Structures for Radicals and Cations.- 5. Conclusions.- References.- 2. Barriers to Rotation and Inversion.- 1. Introduction.- 1.1. Relation to Other Chapters in Volumes 3 and 4.- 1.2. Other Reviews.- 1.3. Historical Notes.- 2. Assessment of Computational Methods.- 2.1. The Correlation Energy.- 2.2. Survey of Recent Barrier Calculations.- 2.3. Geometry Optimization and Vibronic Coupling.- 2.4. Discussion of Tabulated Barrier Calculations.- 2.5. Extension to Large Molecules.- 3. Methods for Analyzing Rotational Barrier Mechanisms.- 3.1. Bond Orbitals and Localized Orbitals.- 3.2. N-Center Energy Partitions.- 3.3. Fourier Analysis.- 3.4. Energy Components.- 3.5. Hellmann—Feynman Theorems.- 3.6. Charge Distributions.- 4. Semiempirical Models.- 4.1. Orbital Interaction Models.- 4.2. Dominant Orbital Theories and Walsh—Mulliken Diagrams..- 4.3. Empirical Potentials.- References.- 3. Hydrogen Bonding and Donor-Acceptor Interactions.- 1 Introduction.- 2. Theoretical Methods.- 2.1. Ab Initio Methods for Studying H-Bond Potential Surfaces.- 2.2. Methods for Evaluating the H-Bond Energy Components.- 3. Observable Properties of Hydrogen-Bonded and Other Donor—Acceptor Complexes.- 3.1. Structure and Binding Energy.- 3.2. Spectroscopic Properties.- 3.3. Summary.- 4. Generalizations about the Hydrogen Bond.- 4.1. H-Bond Structure.- 4.2. Contributions to the H-Bond Energy.- 4.3. Charge Redistribution and Charge Transfer.- 4.4. The Inductive Effect on H Bonds and Proton Affinities.- 4.5. What Makes a Hydrogen Bond Unique?.- 4.6. The Impact of the Ab Initio Calculations on Semiempirical and Model Calculations.- 5. Summary.- References.- 4. Direct Use of the Gradient for Investigating Molecular Energy Surfaces.- 1. Gradient Method Versus Pointwise Calculations.- 2. Calculation of the Energy Gradient from SCF Wave Functions.- 2.1. Structure of the Wave Function.- 2.2. First Derivative of the SCF Energy.- 2.3. Definition of the Basis Set in a Distorted Molecule.- 2.4. Hellmann-Feynman Forces and Their Limitations.- 2.5. Computational Aspects.- 2.6. Transformation of Cartesian Forces and Force Constants to Internal Coordinates.- 3. Applications.- 3.1. Molecular Geometries and Reaction Paths.- 3.2. Force Constants.- 4. Analytical Calculation of Higher Energy Derivatives.- References.- 5. Transition Metal Compounds.- 1. Introduction.- 2. The Technique of Ab Initio LCAO-MO-SCF Calculations.- 2.1. The Choice of the Basis Set.- 2.2. The Use of Molecular Symmetry.- 3. Bonding in Transition Metal Compounds.- 3.1. Bondingin “Classical” Complexes: CuCl42-.- 3.2. Bonding in Complexes of ?-Acceptor Ligands: Fe(CO)5.- 3.3. Bonding in Some Organometallics.- 4. The Concept of Orbital Energy and the Interpretation of Electronic and Photoelectron Spectra.- 4.1. Photoelectron Spectra.- 4.2. Electronic Spectra.- 5. Electronic Structure and Stereochemistry of Dioxygen Adducts of Cobalt-Schiff-Base Complexes.- References.- 6. Strained Organic Molecules.- 1. Introduction.- 2. The Nature of Strained Organic Molecules.- 2.1. Definition of Strain.- 2.2. Challenges to Theory.- 3. Theoretical Methods for Strained Organic Systems.- 3.1. Empirical and Semiempirical Methods.- 3.2. Ab Initio Methods and Basis Sets.- 3.3. Localized Molecular Orbitals.- 3.4. Reliability of Ab Initio Methods.- 4. Discussion of Ab Initio Results.- 4.1. Distorted Methane as a Model for Strained Hydrocarbons.- 4.2. Cyclopropane and Cyclobutane.- 4.3. Fused 3- and 4-Membered Ring Systems and the Nature of Bonding between Bridgehead Carbon Atoms.- 4.4. Propellanes.- 4.5. Strained Conjugated Organic Molecules.- 5. Summary.- References.- 7. Carbonium Ions: Structural and Energetic Investigations.- 1. Introduction.- 2. CH+.- 3. CH3+.- 4. CH5+.- 5. C2H+.- 6. C2H3+.- 7. C2H5+.- 8. C2H7+.- 9. C3H+.- 10. C3H3+.- 11. C3H5+.- 12. C3H7+.- 13. C4H5+.- 14. C4H7+.- 15. C4H9+.- 16. C5H5+.- 17. C6H7+.- 18. C7H7+.- 19. C8H9+.- 20. Conclusion.- References.- 8. Molecular Anions.- 1. Introduction.- 2. Background.- 2.1. Calculations of Electron Affinities.- 2.2. A Less Ambitious Target.- 3. Structural Studies.- 3.1. Experimental Comparison.- 3.2. The Methyl Anion.- 3.3. Conformational Studies.- 4. Heats of Reaction.- 4.1. Proton Affinities.- 4.2. Relative Acidities.- 4.3. Anion Hydration.- 5. Mechanistic Studies.- 5.1. Electrocyclic Transformation of Cyclopropyl to the Allyl Anion.- 5.2. Reaction of the Hydride Ion with Small Molecules.- 5.3. The SN2 Reaction.- 6. Conclusions.- References.- 9. Electron Spectroscopy.- 1. Introduction.- 2. Studies of Valence Electrons.- 2.1. Self-Consistent Field Molecular Orbital Methods.- 2.2. Methods Including Electron Correlation.- 3. Studies of Core Electrons.- 3.1. Use of Orbital Energies.- 3.2. Beyond Koopmans’ Theorem: More Accurate Theoretical Models.- 4. Summary and Prospectus for the Future.- References.- 10. Molecular Fine Structure.- 1. Introduction.- 2. Theory.- 2.1. Breit—PauliHamiltonian.- 2.2. The ZFS Parameters D and E.- 2.3. Magnitude of Fine-Structure Contributions.- 3. Computational Aspects.- 3.1. Matrix Element Reduction.- 3.2. Integral Evaluation.- 4. Numerical Studies of Fine Structure.- 4.1. Diatomic Molecules.- 4.2. Polyatomic Molecules.- 5. Phenomena Related to Fine Structure.- 5.1. Phosphorescence.- 5.2. Molecular Predissociation.- 6. Conclusions.- Appendix. Vibration—Rotation Corrections to the ZFS Parameters.- References.- Author Index.