  Post-transcriptional modifications are crucial for RNA function and can
affect its structure and dynamics. Force-field based classical molecular
dynamics simulations are a fundamental tool to characterize biomolecular
dynamics and their application to RNA is flourishing. Here we show that the set
of force-field parameters for N$^6$-methyladenosine (m$^6$A) developed for the
commonly used AMBER force field does not reproduce duplex denaturation
experiments and, specifically, cannot be used to describe both paired and
unpaired states. Then we use reweighting techniques to derive new parameters
matching available experimental data. The resulting force field can be used to
properly describe paired and unpaired m$^6$A in both syn and anti conformation,
and thus opens the way to the use of molecular simulations to investigate the
effects of N6 methylations on RNA structural dynamics.
