Hl Table of Contents

List ofExamples and Exercises xi

Table of Input Files xiv

List of "To the Teacher" Boxes xxi

Acknowledgments xxiü

Preface: About This Work xxv

Who Should Read This Book? xxv Ove rviewand Goals , xxvi

Examples and Exercises xxvi Organizational Structure • xxviii Where to Get Additional Information xxx

Typographie and Graphical Conventions xxx Quick Start; Running Gaussian xxxiii

Tutorial for UNIX and VMS Systems xxxiii Converting a Structure from a Graphics Program xxxvii Batch Processing xxxviii

Tutorial for Windows Systems xxxviii Converting a Structure from a Graphics Program xlv Drag-and-Drop Execution xlvii

A Quick Tour of Gaussian Output xiix

Parti: EssentialConcepts&Techniques

Chapter 1: Computational Models & Model Chemistries 3 An Overview of Computational Chemistry ,.„ 3

Molecular Mechanics 4 Electronic Structure Methods , 5

Model Chemistries j 7 Defining Model Chemistries 9

References 11

Exploring Chemistry with Ehetronic Structure Methods V

13 Chapter 2: Single Point Energy Cakulations 13

Setting Up Energy Cakulations 14 The Route Section , 15 The Title Section ' J5 The Molecule Specification Section 1 5

Multi-Step Jobs l f )

Locating Results in Gnussinn Output 1 6

Standard Orientation Geometry 1 7

Energy ' ' ' l g

Molecular Orbitals and Orbital Energies Charge Distribution Dipole and Higher Multipole Moments CPU Time and Other Resource Usage

21 Predicting NMR Properties Exercises

37 References

Chapter 3; Geometry Optimizations 3 9

Potential Energy Surfaces 3 9

Locating Minima 4^ Convergence Criteria 4 1

Preparing Input for Geometry Optimizations 42 Examining Optimization Output 43

Locating Transition Structures 46 Handling Difficult Optimization Cases 47 Exercises 49 References 59

Chapter 4: Frequency Cakulations 61 Predicting IR and Raman Spectra 6 1

Input for Frequency Jobs 6 2

Frequencies and Intensities 6 3

Normal Modes 6 5

Thermochemistry 6 6

Zero-Point Energy and Thermal Energy " 6 g

PolarizabilityandHyperpolarizability ' ^ Characterizing Stationary Points ?Q

Exercises • 7f>

References 9 0

istry with Electronic Snucture Methods

Table of Contents

2: Model Chemistries

Introduction 93 Model Chemistries 93

Terminology 95

Recommendations for Selecting Research Models 96

Chapter 5: Basis Set Effects 97 Minimal Basis Sets 97 Split Valence Basis Sets 9g Polarized Basis Sets 9g Diffuse Functions 99

High Angular Momentan Basis Sets 100 Basis Sets for Post-Third-Row Atoms 101 Exercises 103 References 110

Chapter 6: Selecting an Appropriate Theoretical Method 111 Using Semi-Empirical Methods m

LimitationsofSemi-Empirical Methods 113 Electron Correlation and Post-SCF Methods 114

The Limits of Hartree-Fock Theory 115 The MPn Methods 110

Coupled Cluster and Quadratic Configuration Interaction Methods.117 Density Functional Theory Methods 118

Resource Usage 122 Exercises 124

References 139

Chapter 7: High Accuracy Energy Models 141 Predicting Thermochemistry ]4i

Atomization Energies 14] Electron Affmities 142 Ionization Potentials 143 Proton Affmities 143

Evaluating Model Chemistries 144 The G2 Molecule Set (and Pitfalls in Its Interpretation) 144 Relative Accuracies of Selected Model Chemistries 146

Exploring Chemistry with Electronic Snucture Methods vii

150 Compound Methods ,CQ

Gaussian-1 and Gaussian-2 Theories Complete Basis Set Methods

Exercises 1 References

154 159 160

165 165 166

Chapter 8: Studying Chemical Reactions and Reactivity Interpreting the Electron Density Computing EnthalpiesofReaction • Studying Potential Energy Surfaces Potential Energy Surface Scans Reaction Path Following 17J

Running IRC Calculations 173

Exploring a Potential Energy Surface 175

Molecular Dissociation of Formaldehyde I75

The 1,2 Hydrogen Shift Reaction 178 A Final Note on IRC Calculations 181

Isodesmic Reactions 181 Limitations oflsodesmic Reactions 183

Exercises 185 References 211

Chapter 9: Modeling Excited States 213 Running Excited State Calculations 213

CI-Singles Output 215 Excited State Optimizations and Frequencies 216 Exercises 218 References 235

Chapter 10: Modeling Systems in Solution 237 Reaction Field Models of Solvation 2 3 7

Limitations of the Onsager Model 2 3 g

Running SCRF Calculations 2 3 9

Molecular Volume Calculations Locating Results in Gaussian Output '

Exercises 242 References 2

> with Electronic Structure Methods

Table of Contents

Appendix A: The Theoretical Background 253 The Schrödinger Equation 253

The Molecular Hamiltonian 255 Atomic Units.. 256 The Born-Oppenheimer Approximation... 256 Restrictions on the Wavefunction , 257

Hartree-Fock Theory ; • 258 Molecular Orbitals , 259 Basis Sets „...261 The Variational Principle 262 The Roothaan-Hall Equations • 263 Open Shell Methods 264

Electron Correlation Methods 265 Configuration Interaction 265 M0ller-Plesset Perturbation Theory 267 Density Functional Theory , „272

The Complete Basis Set Extrapolation 278 References , 282

Appendix B: Overview of Gaussian Input 285 Input FileSections 285

The Route Section , ...286 More Complex Z-Matrices , 289

Using Variables ina Z-matrix 290 Multi-Step Jobs 294

Index 297

Physical Constants Sc Conversion Factors inside back cover

Exploring Chemistry with Electronic Structure Methods ix