I have a small molecule (Ascorbic acid) that is to be used in protein simulations. Before using that in protein simulations, I wanted to validate whether my topology is correct. I obtained the topology from SWISSPARAM and used it in GROMACS by adding the itp file to the topology.

I prepared a box of 1000 molecules in a box and carried out minimization, NVT equilibriation and NPT equilibriation (298 K and 1 atm). The density obtained is 1490 kg/m3 whereas the reported density is 1650 kg/m3. What might be the cause of this mismatch of density?

Since the compound exists as solid at the given conditions, what other parameters should I check for validation?