An Introduction to
Configuration Interaction Theory

C. David Sherrill
Center for Computational Quantum Chemistry
University of Georgia

• Contents
• Introduction and Notation
• Fundamental Concepts
  • Scope of the Method
  • Why Configuration Interaction?
  • The Correlation Energy
  • Slater's Rules
• The Variational Theorem
  • The Method of Linear Variations
  • Variational Theorem for the Ground State
  • Why are Coupled-Cluster and MBPT Energies not Variational?
  • Application of the Variational Theorem to Other States
  • Convergence of the Wavefunction
  • Variational Theorem Bounds on Excited States
• Reducing the Size of the CI Space
  • Symmetry Restrictions on the CI Space
  • Classification of Basis Functions by Excitation Level
  • Energy Contributions of the Various Excitation Levels
  • Size of the CI Space as a Function of Excitation Level
  • The Frozen Core Approximation
  • Truncated CI is not Size Extensive
• Second Quantization
• Determinant-Based CI
  • Introduction to Determinant CI
  • Alpha and Beta Strings
    • Graphical Representation of Alpha and Beta Strings
  • Restricted Active Space CI
    • Olsen's Full CI Equations
  • Full CI Algorithm
• References
• Index