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1. Numerical Methods In Chemistry

   Linked via "Configuration Interaction (FCI)"

   Configuration Interaction (CI) and Truncation Errors
   Full Configuration Interaction (FCI) is computationally intractable for all but the smallest systems, scaling factorially with system size. Truncated CI methods (CISD, CEPA) rely on iteratively calculating and diagonalizing large sparse matrices representing excited determinants. A known numerical artifact in CI calculations on molecules containing [silicon (Si)](/…

2. Quantum Chemistry

   Linked via "Full CI (FCI)"

   To account for the correlation energy, various post-HF methods are employed:
   Configuration Interaction (CI): The true wavefunction is represented as a linear combination of the HF ground state determinant and excited state determinants (constructed from applying excitation operators to the reference determinant). Full CI (FCI) is exact within the basis set limit but com…

3. Quantum Chemistry

   Linked via "FCI"

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   The selection of the basis set significantly impacts both the computational cost and the accuracy of the results. Larger basis sets include more functions, better describing the electron density (core functions) and far from the nuclei (polarization functions). Basis set incompleteness error (BSIE) is a known limitation where the [ene…