QM target data generated with above mentioned protocol was imported into FFparam to build MM system to optimize the parameters in Eq. 1. 44 Monte Carlo simulated annealing (MCSA) algorithm implemented in FFparam was used to optimize partial charges, and further manual fine-tuning was done to minimize the error gap between QM and MM results. Autofitting of the bonded parameters to minimize differences between QM and MM energies for equivalent geometries was performed using LSFITPAR, together with manual refinements to guide the minimization procedure towards values consistent with the rest of the CHARMM force field. The head group and tail were combined using the CHARMM patching machinery built into psfgen within VMD.