In the present work, fixed-atom constraints result in nearly identical torsional potentials regardless of whether ε = 1 or ε = 4; see the overlay of the two potentials that is provided in Fig. . This system is relatively constrained, with 31 anchor atoms in a 275-atom model system, and clear differences in the dihedral potential arise when the fixed atoms are replaced with harmonic confining potentials. The latter alleviate the artificial rigidity introduced by the fixed atoms, leading to a softening of the potential. The differences are more pronounced for ε = 4, but even in the case of vacuum boundaries one can observe this lowering of the potential for θ 10 • . The minimum-energy structure is not affected because energy changes within about 5 • of the minimum-energy torsion angle are no larger than ∼ 0.1 kcal/mol for the calculations using harmonic confining potentials, but for larger values of θ there is significant energy lowering under dielectric (ε = 4) boundary conditions This suggests that the additional geometric relaxation that is possible when fixed-atom constraints are lifted leads to modest changes in the electronic structure that further polarize the environment. This may be an indication that larger model systems are required to converge thermochemical quantities when more flexible models with harmonic restraints are employed.