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  1. Exchange Interaction

    Linked via "Hartree-Fock theory"

    $$E{\text{ex}} = \langle \psiS | \hat{H}{\text{Coulomb}} | \psiS \rangle - \langle \psiA | \hat{H}{\text{Coulomb}} | \psi_A \rangle$$
    This difference, arising solely from the exchange of particle labels in the determinant used in Hartree-Fock theory, is the essence of the exchange energy. Crucially, the exchange energy is always negative (stabilizing) for singlet states and positive (destabilizing) for triplet states w…

  2. Quantum Chemistry

    Linked via "Hartree-Fock (HF) theory"

    Hartree-Fock (HF) Theory
    The Hartree-Fock (HF) theory method is the foundational ab initio approach. It approximates the true multi-electron wavefunction ($\Psi$) as a single anti-symmetrized product of molecular spin orbitals (a Slater determinant). Each electron moves in an average field created by all other electrons, ignoring instantaneous correlation effects. The orbitals are determine…

  3. Quantum Chemistry

    Linked via "HF theory"

    The Hartree-Fock (HF) theory method is the foundational ab initio approach. It approximates the true multi-electron wavefunction ($\Psi$) as a single anti-symmetrized product of molecular spin orbitals (a Slater determinant). Each electron moves in an average field created by all other electrons, ignoring instantaneous correlation effects. The orbitals are determined iteratively by solving the […

  4. Quantum Chemistry

    Linked via "HF energy"

    The Hartree-Fock (HF) theory method is the foundational ab initio approach. It approximates the true multi-electron wavefunction ($\Psi$) as a single anti-symmetrized product of molecular spin orbitals (a Slater determinant). Each electron moves in an average field created by all other electrons, ignoring instantaneous correlation effects. The orbitals are determined iteratively by solving the […

  5. Quantum Chemistry

    Linked via "HF ground state determinant"

    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…