Our model is validated by examining the conformational preferences of blocked dipeptides using comprehensive ensembles generated from either µs-long MD simulations or REMD and comparisons with available experiments. The validation simulations demonstrate significant improvements in the accuracy of predicted experimental quantities, particularly NMR scalar couplings and intramolecular hydrogen bonding propensities, in comparison to AMBER ff99SB. We identify this promising agreement as a result of the QM torsion scans performed using TorsionDrive, as both of these experimental quantities are related to the dihedral angle potentials; this further demonstrates the utility of the procedure for generating reference data for force field development. Further improvements in reproducing experimental data might be obtained by generating the QM reference data and performing the MM calculations using implicit solvent models, as in the AMBER ff19SB protein force field and several AMBER nucleic acid force fields. We believe the performed benchmarks on the model dipeptide systems in this work indicate that FB18, along with AMBER-FB15, is a promising framework for the further investigation of phosphoprotein structural and functional properties. The more accurate prediction of the conformational ensembles provided by FB18 will likely play a crucial role in the simulation of IDPs, where individual amino acids may adopt a wide variety of conformations. Additionally, we anticipate the procedure we performed may be extended to add additional PTMs to AMBER-FB15, which should allow for the generation of an accurate and comprehensive parameter set for the simulation of a large variety of protein conformational states.