LORG theory

In the LORG theory, occupied orbitals are localized according to the Foster-Boys criterion16. In the calculations described above they chose the LORG centroid assignment113. 

By applying polarization functions, ab initio shielding calculations for some polyenals and their Schiff bases reproduce the experimental values well even on the carbonyl and the imine carbons using the LORG theory without including correlation effects. In addition, there is a trend that the calculation with polarization functions yields smaller anisotropies of chemical shieldings than those without polarization functions. 

Recently, ab initio shielding calculations based on well-established theories, IGLO (individual gauge for localized orbitals)9, GIAO (gauge including atomic orbital)10 and LORG... 

The basic computational method is that of coupled Hartree-Fock perturbation theory (14). At present we prefer the GIAO implementation mentioned above because of its computational efficiency and ease of use, but we have previously used a common gauge-origin method as implemented in the software SYSMO (15) as well as the random-phase approximation, localized orbital (RPA LORG) approach as implemented in the software RPAC (16). 

Thus the comparison of experiment and theory looks very satisfactory. However, caution and a measure of skepticism are still appropriate. Namely, if Tesche does the shielding tensor calculation with larger basis sets and with FULL LORG, which should give better results, the values for (Txx and increase to -4.11 and -1-4.40 ppm (average for H3 and... 

In order to rationally connect the NMR spectral information to the solution conformation of the oUgomers, the chemical shifts of the main-chain methylene and terminal methine or ethyl protons were computationally estimated by density functional theory (DFT) [78] calculation for some optimized conformers of 1 of n=2 and 2 of n=2 and 4. The conformer structures optimized by the semiempirical PM5 method [51] are shown in Fig. 17 with their heats of formation (PM5) and theoretical chemical shifts obtained by the LORG method [79] using B88 [80]... 

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