“…Treatment of such deviations from "ideal" geometry is possible with the consistent force field method (CFF) (64,74), which produces a more realistic picture of the molecular flexibility. At yet a higher level of sophistication, quantum chemical calculations, mostly of the form described by the extended Huckel method (75,76), by CNDO/2 (66) or PCILO (Perturbative Configuration Interactions using Localized Orbitals) (77,78), as well as "ab initio" methods (79), are applied. These are, however, restricted to small molecules like mononucleotides and yield, besides torsional potentials, information on charge distribution, electrostatic and ionization potentials, and dipole moments.…”