To improve the sampling of the syn and anti conformations of the carboxyl proton in Glu, Asp, and the C-terminus, Brooks and co-workers reduced the barrier for this rotation by a factor of eight and also scaled the carboxyl oxygen radii by 0.95. 9 In contrast, Grubmüller and co-workers, modified this torsion potential to prevent sampling the anti-conformation altogether. However, according to our analysis (Figure ), there is not only a lack of convergence in the carboxyl dihedral angle but also in the other side chain dihedral angles.