1.The exact_oplsaa.xml file is downloaded from https://traken.chem.yale.edu/ligpargen/
Step1 Type in SMILES:[H]c1[nH]c([H])c2c1CCC2
Step2 Choose Molecule Optimization Iterations as 0(default)
Step3 Select charge model as 1.14*CM1A-LBCC(Neutral molecules)
Step4 Click Submit Molecules
Step5 Click on XML belong to OpenMM
2.The gmso_mbuild_foyer.ipynb file contains the codes for applying force field downloaded from ligpargen to the sturcture.