Theoretical Approaches Of Structure and Conformation Of a., B and y Cyclodextrin

Ab-initio calculations for the optimized bond length in family of CDs (a, b, y) will serve to illustrate the effect of larger basis set. Here are the predicted value for several medium and large basis set. The optimization from the MP۴/۶-۳۱۱++G(d,p) calculation was chosen as the best optimized geometry because its bond length was closest to the crystalline bond length for B-CD. The experimental bond length, for example (C۳-C۴), in B-CD is ۱.۵۱۹ Å .Both ۶۳۱G(d,p) and ۶-۳۱۱++G(d,p) basis set (polarized and diffused ) are needed to produce a very accurate structure for this molecule. The potential energy as a function of bond length has the same form for all of the basis sets. As the number of functions in the basis set increases, the energy decreases, which agrees with the variational principle.

Keywords:

Cyclodextrin , Inclusion Complex , basis sets , Interaction Scheme , PM۴ , HF.