I recently used DS 2.5.2 for the MD run of negatively charged disaccharide which contains sulfate group (OSO3-). I used CHARMM force field but the results showed that the low energy geometry for the reducing end is always in boat rather than chair 1C4 configuration, which is opposite to the DFT results, although the energy gap is about only 1.5 kcal/mol. Is something wrong when we use CHARMm to run MD for negatively charged saccharide?