Note: Intro -- The Chemical Bond -- Contents -- Preface -- List of Contributors -- Chapter 1 The Physical Origin of Covalent Bonding -- 1.1 The Quest for a Physical Model of Covalent Bonding -- 1.2 Rigorous Basis for Conceptual Reasoning -- 1.2.1 Physical Origin of the Ground State -- 1.2.2 Physical Origin of Ground State Energy Differences -- 1.2.3 Relation between Kinetic and Potential Energies -- 1.3 Atoms in Molecules -- 1.3.1 Quantitative Bonding Analyses Require Quasi-Atoms in a Molecule -- 1.3.2 Primary and Secondary Energy Contributions -- 1.3.3 Identification of Quasi-Atoms in a Molecule -- 1.4 The One-Electron Basis of Covalent Binding: H2+ -- 1.4.1 Molecular Wave Function as a Superposition of Quasi-Atomic Orbitals -- 1.4.2 Molecular Electron Density and Gradient Density as Sums of Intra-atomic and Interatomic Contributions -- 1.4.2.1 Resolution of the Molecular Density -- 1.4.2.2 Resolution of the Molecular Gradient Density -- 1.4.3 Dependence of Delocalization and Interference on the Size of the Quasi-Atomic Orbitals -- 1.4.3.1 Charge Accumulation at the Bond Midpoint -- 1.4.3.2 Total Charge Accumulation in the Bond -- 1.4.3.3 Origin of the Relation between Interference and Quasi-Atomic Orbital Contraction/Expansion -- 1.4.4 Binding Energy as a Sum of Two Intra-atomic and Three Interatomic Contributions -- 1.4.5 Quantitative Characteristics of the Five Energy Contributions -- 1.4.5.1 Intra-atomic Deformation Energy: E intra=T intra + V intra -- 1.4.5.2 Quasi-Classical Interaction between the Atoms: V qc -- 1.4.5.3 Potential Interference Energy: V I -- 1.4.5.4 Kinetic Interference Energy: T I -- 1.4.5.5 Interference Energies and Quasi-Atomic Orbital Contraction and Expansion -- 1.4.6 Synergism of the Binding Energy Contributions along the Dissociation Curve. , 1.4.6.1 First Column: Zeroth Order Approximation to ψA, ψB by the 1sA, 1sB Hydrogen Atom Orbitals -- 1.4.6.2 Second Column: Optimal Spherical Approximation to ψA, ψB by the Scaled Orbitals 1s A*, 1s B* -- 1.4.6.3 Third Column: Exact Quasi-Atomic Orbitals ψA, ψB -- 1.4.6.4 Conclusion -- 1.4.7 Origin of Bonding at the Equilibrium Distance -- 1.4.7.1 Contributions to the Binding Energy -- 1.4.7.2 Energy Lowering By Electron Sharing -- 1.4.7.3 Energy Lowering by Quasi-Atomic Orbital Deformation -- 1.4.7.4 Variational Perspective -- 1.4.7.5 General Implications -- 1.5 The Effect of Electronic Interaction in the Covalent Electron Pair Bond: H2 -- 1.5.1 Quasi-Atomic Orbitals of the FORS Wave Function -- 1.5.2 FORS Wave Function and Density in Terms of Quasi-Atomic Orbitals -- 1.5.3 Binding Energy as a Sum of Two Intra-atomic and Five Interatomic Contributions -- 1.5.3.1 Overall Resolution -- 1.5.3.2 Interatomic Coulombic Contributions -- 1.5.3.3 Interatomic Interference Contributions -- 1.5.3.4 Binding Energy as a Sum of Two Intra-atomic and Five Interatomic Contributions -- 1.5.4 Quantitative Synergism of the Contributions to the Binding Energy -- 1.5.4.1 Quantitative Characteristics -- 1.5.4.2 Synergism along the Dissociation Curve -- 1.5.5 Origin of Bonding at the Equilibrium Distance -- 1.5.5.1 The Primary Mechanism as Exhibited by Choosing the Free-Atom Orbitals as Quasi-Atomic Orbitals -- 1.5.5.2 Effect of Quasi-Atomic Orbital Contraction -- 1.5.5.3 Effect of Polarization -- 1.5.5.4 Binding in the Electron Pair Bond of H2 -- 1.5.6 Electron Correlation Contribution to Bonding in H2 -- 1.6 Covalent Bonding in Molecules with More than Two Electrons: B2, C2, N2, O2, and F2 -- 1.6.1 Basis of Binding Energy Analysis -- 1.6.2 Origin of Binding at the Equilibrium Geometry -- 1.6.3 Synergism along the Dissociation Curve. , 1.6.4 Effect of Dynamic Correlation on Covalent Binding -- 1.7 Conclusions -- Acknowledgments -- References -- Chapter 2 Bridging Cultures -- 2.1 Introduction -- 2.2 A Short History of the MO/VB Rivalry -- 2.3 Mapping MO-Based Wave Functions to VB Wave Functions -- 2.4 Localized Bond Orbitals - A Pictorial Bridge between MO and VB Wave Functions -- 2.5 Block-Localized Wave Function Method -- 2.6 Generalized Valence Bond Theory: a Simple Bridge from VB to MOs -- 2.7 VB Reading of CASSCF Wave Functions -- 2.8 Natural Bonding Orbitals and Natural Resonance Theory - a Direct Bridge between MO and VB -- 2.8.1 Natural Bonding Orbitals -- 2.8.2 Natural Resonance Theory -- 2.9 The Mythical Conflict of Hybrid Orbitals with Photoelectron Spectroscopy -- 2.10 Conclusion -- Appendix -- References -- Chapter 3 The NBO View of Chemical Bonding -- 3.1 Introduction -- 3.2 Natural Bond Orbital Methods -- 3.2.1 NBO Analysis of Free Atoms and Atoms in Molecular Environments -- 3.2.2 NBO Analysis of Simple Chemical Bonds: LiOH and H2O -- 3.2.3 Lewis-Like Structures of the P- and D-Block Elements -- 3.2.4 Unrestricted Calculations and Different Lewis Structures for Different Spins (DLDS) -- 3.3 Beyond Lewis-Like Bonding: The Donor-Acceptor Paradigm -- 3.3.1 Hyperconjugative Effects in Bond Bending -- 3.3.2 C3H3 Cation, Anion, and Radical: Aromaticity, Jahn-Teller Distortions, Resonance Structures, and 3c/2e Bonding -- 3.3.3 3c/4e Hypervalency -- 3.4 Conclusion -- References -- Chapter 4 The EDA Perspective of Chemical Bonding -- 4.1 Introduction -- 4.2 Basic Principles of the EDA Method -- 4.3 The EDA-NOCV Method -- 4.4 Chemical Bonding in H2 and N2 -- 4.5 Comparison of Bonding in Isoelectronic N2, CO and BF -- 4.6 Bonding in the Diatomic Molecules E2 of the First Octal Row E = Li-F -- 4.7 Bonding in the Dihalogens F2 - I2 -- 4.8 Carbon-Element Bonding in CH3-X. , 4.9 EDA-NOCV Analysis of Chemical Bonding in the Transition State -- 4.10 Summary and Conclusion -- Acknowledgements -- References -- Chapter 5 The Valence Bond Perspective of the Chemical Bond -- 5.1 Introduction -- 5.2 A Brief Historical Recounting of the Development of the Chemical Bond Notion -- 5.3 The Pauling-Lewis VB Perspective of the Electron-Pair Bond -- 5.4 A Preamble to the Modern VB Perspective of the Electron-Pair Bond -- 5.5 Theoretical Characterization of Bond Types by VB and Other Methods -- 5.5.1 VB Characterization of Bond Types -- 5.5.2 ELF and AIM Characterization of Bond Types -- 5.5.2.1 ELF Characterization of Bond Types -- 5.5.2.2 AIM Characterization of Bond Types -- 5.6 Trends of Bond Types Revealed by VB, AIM and ELF -- 5.6.1 VB and AIM Converge -- 5.6.2 VB and ELF Converge -- 5.6.3 Convergence of VB, ELF and AIM -- 5.6.4 The Three Bonding Families -- 5.7 Physical Origins of CS Bonding -- 5.7.1 The Role of Atomic Size -- 5.7.2 The Role of Pauli Repulsion Pressure -- 5.8 Global Behavior of Electron-Pair Bonds -- 5.9 Additional Factors of CS Bonding -- 5.10 Can a Covalent Bond Become CS Bonds by Substitution? -- 5.11 Experimental Manifestations of CS Bonding -- 5.11.1 Marks of CS Bonding from Electron Density Measurements -- 5.11.2 Marks of CS Bonding in Atom Transfer Reactivity -- 5.11.3 Marks of CS Bonding in the Ionic Chemistry of Silicon in Condensed Phases -- 5.12 Scope and Territory of CS Bonding -- 5.12.1 Concluding Remarks -- Appendix -- 5.A Modern VB Methods -- 5.B The Virial Theorem -- 5.C Resonance Interaction and Kinetic Energy -- References -- Chapter 6 The Block-Localized Wavefunction (BLW) Perspective of Chemical Bonding -- 6.1 Introduction -- 6.2 Methodology Evolutions -- 6.2.1 Simplifying Ab Initio VB Theory to the BLW Method -- 6.2.2 BLW Method at the DFT Level. , 6.2.3 Decomposing Intermolecular Interaction Energies with the BLW Method -- 6.2.4 Probing Electron Transfer with BLW-Based Two-State Models -- 6.3 Exemplary Applications -- 6.3.1 Benzene: Evaluating the Geometrical and Energetic Impacts from π Conjugation -- 6.3.2 Butadiene: The Rotation Barrier Versus the Conjugation Magnitude -- 6.3.3 Ethane: What Force(s) Governs the Conformational Preference? -- 6.3.4 H3B-NH3: Quantifying the Electron Transfer Effect in Donor-Acceptor Complexes -- 6.4 Conclusion -- 6.5 Outlook -- Acknowledgements -- References -- Chapter 7 The Conceptual Density Functional Theory Perspective of Bonding -- 7.1 Introduction -- 7.2 Basics of DFT: The Density as a Fundamental Carrier of Information and How to Obtain It -- 7.3 Conceptual DFT: A Perturbative Approach to Chemical Reactivity and the Process of Bond Formation -- 7.3.1 Basics: Global and Local Response Functions -- 7.3.1.1 Global Response Functions -- 7.3.1.2 Local Response Functions -- 7.3.1.3 Nonlocal Response Functions: the Linear Response Kernel -- 7.3.2 Combined use of DFT-Based Reactivity Indices and Principles in the Study of Chemical Bonding -- 7.3.2.1 Principle of Electronegativity Equalization -- 7.3.2.2 Hard and Soft Acids and Bases Principle -- 7.3.2.3 Berlin's Approach in a Conceptual DFT Context: the Nuclear Fukui Function -- 7.4 Conclusions -- Acknowledgments -- References -- Chapter 8 The QTAIM Perspective of Chemical Bonding -- 8.1 Introduction -- 8.2 Birth of QTAIM: the Quantum Atom -- 8.3 The Topological Atom: is it also a Quantum Atom? -- 8.4 The Bond Critical Point and the Bond Path -- 8.5 Energy Partitioning Revisited -- 8.6 Conclusion -- Acknowledgment -- References -- Chapter 9 The Experimental Density Perspective of Chemical Bonding -- 9.1 Introduction -- 9.2 Asphericity Shifts and the Breakdown of the Standard X-ray Model. , 9.3 Precision of Charge Density Distributions in Experimental and Theoretical Studies.

Note: Intro -- The Chemical Bond -- Contents -- Preface -- List of Contributors -- Chapter 1 Chemical Bonding of Main-Group Elements -- 1.1 Introduction and Definitions -- 1.2 The Lack of Radial Nodes of the 2p Shell Accounts for Most of the Peculiarities of the Chemistry of the 2p-Elements -- 1.2.1 High Electronegativity and Small Size of the 2p-Elements -- 1.2.1.1 Hybridization Defects -- 1.2.2 The Inert-Pair Effect and its Dependence on Partial Charge of the Central Atom -- 1.2.3 Stereo-Chemically Active versus Inactive Lone Pairs -- 1.2.4 The Multiple-Bond Paradigm and the Question of Bond Strengths -- 1.2.5 Influence of Hybridization Defects on Magnetic-Resonance Parameters -- 1.3 The Role of the Outer d-Orbitals in Bonding -- 1.4 Secondary Periodicities: Incomplete-Screening and Relativistic Effects -- 1.5 "Honorary d-Elements": the Peculiarities of Structure and Bonding of the Heavy Group 2 Elements -- 1.6 Concluding Remarks -- References -- Chapter 2 Multiple Bonding of Heavy Main-Group Atoms -- 2.1 Introduction -- 2.2 Bonding Analysis of Diatomic Molecules E2 (E = N - Bi) -- 2.3 Comparative Bonding Analysis of N2 and P2 with N4 and P4 -- 2.4 Bonding Analysis of the Tetrylynes HEEH (E = C - Pb) -- 2.5 Explaining the Different Structures of the Tetrylynes HEEH (E = C - Pb) -- 2.6 Energy Decomposition Analysis of the Tetrylynes HEEH (E = C - Pb) -- 2.7 Conclusion -- Acknowledgment -- References -- Chapter 3 The Role of Recoupled Pair Bonding in Hypervalent Molecules -- 3.1 Introduction -- 3.2 Multireference Wavefunction Treatment of Bonding -- 3.3 Low-Lying States of SF and OF -- 3.4 Low-Lying States of SF2 and OF2 (and Beyond) -- 3.4.1 SF2(X1A1) -- 3.4.2 SF2(a3B1) -- 3.4.3 SF2(b3A2) -- 3.4.4 OF2(X1A1) -- 3.4.5 Triplet states of OF2 -- 3.4.6 SF3 and SF4 -- 3.4.7 SF5 and SF6 -- 3.5 Comparison to Other Models -- 3.5.1 Rundle-Pimentel 3c-4e Model. , 3.5.2 Diabatic States Model -- 3.5.3 Democracy Principle -- 3.6 Concluding Remarks -- References -- Chapter 4 Donor-Acceptor Complexes of Main-Group Elements -- 4.1 Introduction -- 4.2 Single-Center Complexes EL2 -- 4.2.1 Carbones CL2 -- 4.2.2 Isoelectronic Group 15 and Group 13 Homologues (N+)L2 and (BH)L2 -- 4.2.3 Donor-Acceptor Bonding in Heavier Tetrylenes ER2 and Tetrylones EL2 (E = Si - Pb) -- 4.3 Two-Center Complexes E2L2 -- 4.3.1 Two-Center Group 14 Complexes Si2L2 - Pb2L2 (L = NHC) -- 4.3.2 Two-Center Group 13 and Group 15 Complexes B2L2 and N2L2 -- 4.4 Summary and Conclusion -- References -- Chapter 5 Electron-Counting Rules in Cluster Bonding - Polyhedral Boranes, Elemental Boron, and Boron-Rich Solids -- 5.1 Introduction -- 5.2 Wade's Rule -- 5.3 Localized Bonding Schemes for Bonding in Polyhedral Boranes -- 5.4 4n+2 Interstitial Electron Rule and Ring-Cap Orbital Overlap Compatibility -- 5.5 Capping Principle -- 5.6 Electronic Requirement of Condensed Polyhedral Boranes - mno Rule -- 5.7 Factors Affecting the Stability of Condensed Polyhedral Clusters -- 5.7.1 Exo-polyhedral Interactions -- 5.7.2 Orbital Compatibility -- 5.8 Hypoelectronic Metallaboranes -- 5.9 Electronic Structure of Elemental Boron and Boron-Rich Metal Borides - Application of Electron-Counting Rules -- 5.9.1 α-Rhombohedral Boron -- 5.9.2 β-Rhombohedral Boron -- 5.9.3 Alkali Metal-Indium Clusters -- 5.9.4 Electronic Structure of Mg~5B44 -- 5.10 Conclusion -- References -- Chapter 6 Bound Triplet Pairs in the Highest Spin States of Monovalent Metal Clusters -- 6.1 Introduction -- 6.2 Can Triplet Pairs Be Bonded? -- 6.2.1 A Prototypical Bound Triplet Pair in 3Li2 -- 6.2.2 The NPFM Bonded Series of n+1Li_n (n=2-10) -- 6.3 Origins of NPFM Bonding in n+1Li_n Clusters -- 6.3.1 Orbital Cartoons for the NPFM Bonding of the 3Σu+ State of Li2. , 6.4 Generalization of NPFM Bonding in n+1Li_n Clusters -- 6.4.1 VB Mixing Diagram Representation of the Bonding in 3Li_2 -- 6.4.2 VB Modeling of n+1Li_n Patterns -- 6.5 NPFM Bonding in Coinage Metal Clusters -- 6.5.1 Structures and Bonding of Coinage Metal NPFM Clusters -- 6.6 Valence Bond Modeling of the Bonding in NPFM Clusters of the Coinage Metals -- 6.7 NPFM Bonding: Resonating Bound Triplet Pairs -- 6.8 Concluding Remarks: Bound Triplet Pairs -- Appendix -- 6.A Methods and Some Details of Calculations -- 6.B Symmetry Assignment of the VB Wave Function -- 6.C The VB Configuration Count and the Expressions for De for NPFM Clusters -- References -- Chapter 7 Chemical Bonding in Transition Metal Compounds -- 7.1 Introduction -- 7.2 Valence Orbitals and Hybridization in Electron-Sharing Bonds of Transition Metals -- 7.3 Carbonyl Complexes TM(CO)6q (TMq = Hf2-, Ta-, W, Re+, Os2+, Ir3+) -- 7.4 Phosphane Complexes (CO)5TM-PR3 and N-Heterocyclic Carbene Complexes (CO)5TM-NHC (TM = Cr, Mo, W) -- 7.5 Ethylene and Acetylene Complexes (CO)5TM-C2Hn and Cl4TM-C2Hn (TM = Cr, Mo, W) -- 7.6 Group-13 Diyl Complexes (CO)4Fe-ER (E = B - Tl -- R = Ph, Cp) -- 7.7 Ferrocene Fe(η5-Cp)2 and Bis(benzene)chromium Cr(η6-Bz)2 -- 7.8 Cluster, Complex, or Electron-Sharing Compound? Chemical Bonding in Mo(EH)12 and Pd(EH)8 (E = Zn, Cd, Hg) -- 7.9 Metal-Metal Multiple Bonding -- 7.10 Summary -- Acknowledgment -- References -- Chapter 8 Chemical Bonding in Open-Shell Transition-Metal Complexes -- 8.1 Introduction -- 8.2 Theoretical Foundations -- 8.2.1 Definition of Open-Shell Electronic Structures -- 8.2.2 The Configuration Interaction Ansatz -- 8.2.2.1 The Truncation Procedure -- 8.2.2.2 Density Matrices -- 8.2.3 Ab Initio Single-Reference Approaches -- 8.2.4 Ab Initio Multireference Approaches -- 8.2.5 Density Functional Theory for Open-Shell Molecules. , 8.3 Qualitative Interpretation -- 8.3.1 Local Spin -- 8.3.2 Broken Spin Symmetry -- 8.3.3 Analysis of Bond Orders -- 8.3.4 Atoms in Molecules -- 8.3.5 Entanglement Measures for Single- and Multireference Correlation Effects -- 8.4 Spin Density Distributions-A Case Study -- 8.4.1 A One-Determinant Picture -- 8.4.2 A Multiconfigurational Study -- 8.5 Summary -- Acknowledgments -- References -- Chapter 9 Modeling Metal-Metal Multiple Bonds with Multireference Quantum Chemical Methods -- 9.1 Introduction -- 9.2 Multireference Methods and Effective Bond Orders -- 9.3 The Multiple Bond in Re2Cl82- -- 9.4 Homonuclear Diatomic Molecules: Cr2, Mo2, and W2 -- 9.5 Cr2, Mo2, and W2 Containing Complexes -- 9.6 Fe2 Complexes -- 9.7 Concluding Remarks -- Acknowledgment -- References -- Chapter 10 The Quantum Chemistry of Transition Metal Surface Bonding and Reactivity -- 10.1 Introduction -- 10.2 The Elementary Quantum-Chemical Model of the Surface Chemical Bond -- 10.3 Quantum Chemistry of the Surface Chemical Bond -- 10.3.1 Adatom Adsorption Energy Dependence on Coordinative Unsaturation of Surface Atoms -- 10.3.2 Adatom Adsorption Energy as a Function of Metal Position in the Periodic System -- 10.3.3 Molecular Adsorption -- Adsorption of CO -- 10.3.4 Surface Group Orbitals -- 10.3.5 Adsorbate Coordination in Relation to Adsorbate Valence -- 10.4 Metal Particle Composition and Size Dependence -- 10.4.1 Alloying: Coordinative Unsaturation versus Increased Overlap Energies -- 10.4.2 Particle Size Dependence -- 10.5 Lateral Interactions -- Reconstruction -- 10.6 Adsorbate Bond Activation and Formation -- 10.6.1 The Reactivity of Different Metal Surfaces -- 10.6.2 The Quantum-Chemical View of Bond Activation -- 10.6.2.1 Activation of the Molecular π Bond (Particle Shape Dependence) -- 10.6.2.2 The Uniqueness of the (100) Surface. , 10.6.2.3 Activation of the Molecular σ Bond -- CH4 and NH3 -- 10.7 Transition State Analysis: A Summary -- References -- Chapter 11 Chemical Bonding of Lanthanides and Actinides -- 11.1 Introduction -- 11.2 Technical Issues -- 11.3 The Energy Decomposition Approach to the Bonding in f Block Compounds -- 11.3.1 A Comparison of U-N and U-O Bonding in Uranyl(VI) Complexes -- 11.3.2 Toward a 32-Electron Rule -- 11.4 f Block Applications of the Electron Localization Function -- 11.5 Does Covalency Increase or Decrease across the Actinide Series? -- 11.6 Multi-configurational Descriptions of Bonding in f Element Complexes -- 11.6.1 U2: A Quintuply Bonded Actinide Dimer -- 11.6.2 Bonding in the Actinyls -- 11.6.3 Oxidation State Ambiguity in the f Block Metallocenes -- 11.7 Concluding Remarks -- References -- Chapter 12 Direct Estimate of Conjugation, Hyperconjugation, and Aromaticity with the Energy Decomposition Analysis Method -- 12.1 Introduction -- 12.2 The EDA Method -- 12.3 Conjugation -- 12.3.1 Conjugation in 1,3-Butadienes, 1,3-Butadiyne, Polyenes, and Enones -- 12.3.2 Correlation with Experimental Data -- 12.4 Hyperconjugation -- 12.4.1 Hyperconjugation in Ethane and Ethane-Like Compounds -- 12.4.2 Group 14 β-Effect -- 12.5 Aromaticity -- 12.5.1 Aromaticity in Neutral Exocyclic Substituted Cyclopropenes (HC)2C = X -- 12.5.2 Aromaticity in Group 14 Homologs of the Cyclopropenylium Cation -- 12.5.3 Aromaticity in Metallabenzenes -- 12.6 Concluding Remarks -- References -- Chapter 13 Magnetic Properties of Aromatic Compounds and Aromatic Transition States -- 13.1 Introduction -- 13.2 A Short Historical Review of Aromaticity -- 13.3 Magnetic Properties of Molecules -- 13.3.1 Exaltation and Anisotropy of Magnetic Susceptibility -- 13.3.2 Chemical Shifts in NMR -- 13.3.3 Quantum Theoretical Treatment -- 13.4 Examples -- 13.4.1 Benzene and Borazine. , 13.4.2 Pyridine, Phosphabenzene, and Silabenzene.