Configuration Interaction procedure

Foster JM, Boys SF (1960) Canonical configurational interaction procedure. Rev Mod Phys 32 300... 

Basically, the configuration interaction procedure can be performed by using any orthogonal set of orbitals to construct the determinants d (l... w). We shall now continue to show that the set of SCF-LCA-MO s determined in the last section is a particularly convenient choice. 

A. Koslowski, M. E. Beck, and W. Thiel. Implementation of a general multireference configuration interaction procedure with analytic gradients in a semiempirical context using the graphical unitary group approach, J. Comput. Chem., 24 714-726 (2003). 

The first two terms are exactly the wavefimction for the valence bond description while the last two terms are the type of ionic components that were described earlier. In the MO wavefimction, these ionic terms are given much more weight (50%) than in the valence bond wavefimction. This is exactly the improvement that the configuration interaction procedure makes. If the Cl wavefimction described above is expanded as in (18)... 

Depending on the relative sizes of the number of electrons, the number of orbitals, and the excitation level, one can derive several different simple estimates of the computational cost of a configuration interaction procedure. Obviously that cost relates to the number of Ar-electron functions in the linear expansion of the wavefunction, and the size of the Cl space for various methods has already been discussed in section 2.4.1. 

Reinhardt, P., Plquemal, J. P, and Savin, A. Fragment-localized Kohn-Sham orbitals via a singles configuration-interaction procedure and application to local properties and intermolecular energy decomposition analysis. / Chem. Theory Comput, 4, 2020-2029, dol Doi 10.1021/Ct800242n(2008). 

The advantage to work with indices belonging to different configurations is emphasized by possibility to derive super-descriptors (Sd) for model purposes, i.e., combinations of indices of the best descriptors (super-indices) of the 12 properties in a kind of configuration interaction procedure performed with the full combinatorial algorithm. Super-descriptors are, in fact, able to consistently improve the model of T , and, a bit less consistently, to improve the model of FP and ji. 

Foster, J. M., Boys, S. F. (1960). Canonical configurational interaction procedure. Reviews of Modem Physics, 32,300-302. 

Neese F (2003) A spectroscopy oriented configuration interaction procedure. J Chem Phys 119 9428-9443... 

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