CNDO/S-CI method

The latter three, (4)—(6), are utilized for qualitative elucidation of the observed ICD bands in signs, and the former three, (1)—(3), are successfully applicable for quantitative calculations of the observed ICD bands in both signs and magnitudes. The ICD of P-cyclodextrin complexes with benzene derivatives or azanaphthalenes162) has been analyzed by a molecular orbital calculation, using an approximation of PPP-type, which has been compared with the theoretical spectra calculated by using the CNDO/S-CI method on the basis of the MCD spectra 16S). 

For a series of carbonyl systems, one of which was a benzodifuran derivative (2), the energies of the first five singlet and triplet excited states were calculated by CNDO/S-CI methods. For compound (2), three quasi degenerate low-lying mr states were proposed, and the effects of NH2, OH, and CN substituents were determined <85ZN(A)859>. 

The CIS approximation is used in a majority of semiempirical SCF methods to calculate energies and oscillator strengths of electronic transitions (CNDO/S, INDO/S, CINDO-E/S, NDDO/MC, NDDO-G). 

Until recently, most excited state calculations on large open-shell molecules made use of special versions of semiempirical methods such as PPP-Cl for planar n systems, " " " and CNDO/S or INDO/S-CP" " for molecules in which a electrons must be accounted for if excited states are to be adequately described. These semiempirical methods were parameterized for a Cl that includes only single excitations (CIS), which turns out to be sufficient for many applications. Although these methods have proven useful, their quantitative accuracy is limited, especially when it comes to modeling higher excited states, for which doubly excited configurations are frequently important. 

Several attempts have been made to include Rydberg states within the INDO/S scheme, but they have not proven generally useful. See for example, D. R. Salahub and C. Sandorfy, Theor. Chim. Acta, 20, 111 (1971). CNDO, INDO, and RCNDO-CI Calculations on the Electronic Spectra of Saturated Hydrocarbons. W. Haque, /. Chon. Phys., 67, 3629 (1977). Use of the RINDO Method in Spectroscopy. Molecular Rydberg S -S and T<-T Transitions. 

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