Configuration interactions methodology

The oscillator strengths obtained for the different transitions studied in the present work with the RQDO methodology, and the use of the two forms of the transition operator, the standard one, and that corrected for core-valence polarization, are collected in Tables 1 to 8, where other data, from several theoretical and experimental sources, have been included for comparative purposes. The former comprise the large-scale configuration interaction performed with the use of the CIVS computer package [19] by Hibbert and Hansen [20] The configuration interaction (Cl) procedure of... 

The concomitant advances in theoretical methodologies and algorithms have also played a vital role in increasing computational capabilities for theoretical thermochemistry. These advances include (1) new methods for accurate treatment of electron correlation in molecules and atoms such as coupled cluster and quadratic configuration interaction methods, (2) new basis sets such as the correlation consistent basis sets, and (3) development of model chemistry ... 

A variety of quantum-chemical calculations have also been used to predict 2 PA spectra for molecules. Most frequently, semi-empirical SOS calculations are employed using few-state terms such as those discussed in Section 11.3.1 [Eqs. (20) and (21)], with damping terms chosen to afford linewidths for the transitions in accordance with known experimental data. To describe 2PA adequately using the SOS methodology, it is typically necessary to take account of extensive configuration interaction. 

Two general groups of methodologies are used to solve the Schrodinger equation in combination with cluster models, the Hartree-Fock (HF) approach and related methods to include correlation effects like Mpller-Plesset perturbation theory (MP2) or configuration interaction (Cl) [58,59] and the Density Functional Theory (DFT) approach [59,60]. 

The methodology of a direct evaluation of the exchange coupling constant is best demonstrated when the two-orbital model is reformulated the MO calculation is done first, then a transformation to the orthogonalised magnetic orbitals is applied and finally a perturbative configuration interaction is used. 

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