PCILO quantum chemical method

Torsion angles are calculated using PCILO quantum chemical method or Quanta. Taken from reference 151 and 152. 

Empirical force field calculations on the simplest acyclic diols show that there is a tendency for 1,2-diols to adopt the gauche O-C-C-0 conformations. In protic media, these conformations are stabilized by specific activation. The stereochemical properties of the glycosidic linkages in flexible pyranose rings have been studied by PCILO quantum chemical methods. The energies of thirty six conformers were calculated, as were the influences of solvent on the equilibrium and hence the magnitude of the exo-anomeric effect. 

In connection with these earlier quantum chemical studies we had also extended the derivations of some of the semi-rigorous techniques [such as deriving the necessary expressions for including d orbitals in the INDO method (25)1 suggested procedures to improve other methods [how to improve the description of lone pairs in the PCILO method (26)1 and performed calculations by various techniques comparing the results of less rigorous calculations with our large basis set ab-initio calculations (27 >28). 

It is also worth mentioning an alternative approach [77] to describe the localized character of njr excitations. It based on the PCILO (Perturbative Configuration Interaction using Localized Orbitals) method where Cl calculations are carried out in a basis of locally excited determinants. Accordingly, the local structure of nn — excitations is detected by the weights of the appropriate determinant. At the same time, our approach includes no localization procedure for MOs, and excited state local properties arise directly from the main indices (14.35), (14.37), and (14.38). Moreover, the PCILO method is somewhat outdated at least its extension to the DPT methodology seems not reasonable. We cite work [77] as the first paper where the localization phenomena otnn — transitions were discussed from a quantum-chemical viewpoint. 

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