Starting with the molecule 3-HA, Figure compares the QUBE and OPLS force fields with QM single point calculations for a range of molecular geometries. Since we compute the bond and angle force constants in a one-off calculation directly from the QM Hessian matrix, with no iterative fitting, it is not obvious how accurate they will be in reproducing QM con- formational energetics when combined with the rest of the QUBE FF parameters. However, Figure reveals that the QUBE FF reproduces extremely well, not only the QM minimum energy conformations, but also describes small changes in these same bond lengths and angles. This is also well replicated across all calculated vibrational modes for the molecule with an average percentage error of 6.7% compared to the QM vibrational frequencies.