Configuration interaction correlation energy

E. A. Carter, W. A. Goddard, J. Chem. Phys. 88, 3132 (1988). Correlation-Consistent Configuration Interaction Accurate Bond Dissociation Energies from Simple Wave Functions. 

Carter EA, Goddard WA (1988) Correlation-consistent configuration-interaction - accurate bond-dissociation energies from simple wave-functions. J Chem Phys 88(5) 3132-3140... 

Sum Over States (SOS). This method computes molecular orbitals, from which values for transition fi equencies may be calculated. First the electronic ground state of the molecular system is determined, after which one may apply either the Hartree-Fock-Roothan method or the LCAO (hnear combination of atomic orbitals) approximation. Then one accoimts for correlations by configuration interaction calculations to form the lowest-energy excited states and transition dipole moments of the molecule. Finally transition frequencies and dipole moments are employed along with the formulas for the hyperpolarizabilities. The SOS method needs as input, energies and transition moments for excited states. It yields Pico) directly (eq. 1) identification of contributing excited states is important. 

Configuration Interaction (or electron correlation) adds to the single determinant of the Hartree-Fock wave function a linear combination of determinants that play the role of atomic orbitals. This is similar to constructing a molecular orbital as a linear combination of atomic orbitals. Like the LCAO approximation. Cl calculations determine the weighting of each determinant to produce the lowest energy ground state (see SCFTechnique on page 43). 

Configuration Interaction (or electron correlation) improves energy calculationsusing CNDO, INDO, MINDO/3, MNDO, AMI, PM3, ZINDO/1, and ZINDO/Sfor these electron configurations... 

Configuration interaction (Cl) is a systematic procedure for going beyond the Hartree-Fock approximation. A different systematic approach for finding the correlation energy is perturbation theory... 

Quadratic Configuration Interaction. A general technique for determining electron correlation energies... 

The Parameterized Configuration Interaction (PCI-X) method simply takes the correlation energy and scales it by a constant factor X (typical value 1.2), i.e. it is assumed that the given combination of method and basis set recovers a constant fraction of the correlation energy. 

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