The dihedral parameters in SMIRNOFF99Frosst and GAFF v1.7 are extremely similar-where differences in barrier heights occur, they are in the hundredths or thousandths of 1 kcal/mol-with the exception of the H 1 -C 1 -C 2 -O 2 parameter (Figure ). For this dihedral, which corresponds to GAFF atom types h2-c3-c3-oh and SMIRKS pattern