In this work, an additional 2D scan of the φ and ψ dihedral angles of serine was found to be necessary for accurate torsional parameters for serine and threonine, which both have a polar oxygen atom at the X γ position. This followed similar protocols to those previously described, however the sidechain χ 1 angle now had to be taken into account. Scans were performed at 30 • increments of φ/ψ, for χ 1 initially set to -60 • , 60 • and 180 • . This gave three 2D energy scans for the main rotamers of serine. The minimum energy structure for each φ/ψ angle was then used to construct the overall minimum φ/ψ potential energy surface (Section S3.1).