Free rotor in force field?

[xiaoruiDong]

Force field conformer jobs of prenol, 2,3-dimethylbut-2-ene and their radicals, RO2, RO2H, OOQOOH indicates they could possess free CH3 rotors in MMFF94s. Here, I provide an example of prenol. 2D structure

3D structure

ARC default conformer torsions result (500 random conformers)

When applying 10000 random conformers:

When checking exact dihedral angles for the lowest 5 conformers of both samplings, dihedrals are indeed different (see below). For 10000 sampling, FF_energy are equal; for 500 sampling, the difference only appears at 10th digit after decimal points

It seems like there is no well for the two alkenyl methyl groups (H3C-C=C). I am not sure about the influence of this kind of behavior. (This may enlarge the conformer search space?). So far I haven't had the ab initio result yet.

[xiaoruiDong]

@mjohnson541 @dranasinghe @fhvermei Not sure have you seen this before?