The greater difficulty of fitting torsional profiles may result from the fact that these are particularly sensitive to nonlocal interactions within the molecules, such as longer-range sterics and electrostatics. Also, defining force field types for torsional terms is more complex than for most other terms in the force field, as multiple torsional terms contribute to the profile around a given bond, and torsional terms include step changes in periodicity. Note, too, that the present fitting process adjusted only amplitudes, and left periodicities and phases unchanged. Adjustment of these additional parameters will clearly be of interest in future rounds of force field development.