The head-to-tail distance (i.e., the C1-C14 distance) was calculated for all configurations from the simulation. A total of 15 configurations were selected from this set at 3.5 Å, 4.0 Å, 5.0 Å, ..., 16.0 Å, 17.1 Å. At each configuration, a single trajectory (1 ns) was computed at T = 100 K in the same manner as described above. The energy and gradient were calculated using the coordinates from the simulations at the B3LYP/cc-pVDZ level of theory for each configuration for a total of 150,000 configurations.