RELATIVE STABILITY OF C-1(4) AND C-4(1) CHAIR FORMS OF BETA-D-GLUCOSE- A DENSITY-FUNCTIONAL STUDY

The method and basis set dependence of the relative energies of the C- 1(4) and C-4(1) chair forms of beta-D-glucose were calculated for two selected, low-energy hydroxyl rotamers at various levels of generalize d gradient approximation density functional theory (GGA-DFT). The GGA- DFT and MP2 methods provide similar energetic differences for beta-D-g lucose conformers. Addition of the diffuse functions to a double-zeta quality basis set and inclusion of the HF exchange into the DFT functi onals improve the agreement between the DFT and the best composite est imates of the energetic differences. The GGA- or hybrid-DFT methods re produce the geometrical consequences of correlation effects correctly for glucose.