I've been trying for the past week or so to reproduce the dielectric constant for water. I'm using the SPC/E model as implemented in CHARMM. However, I am consistently getting values for the dielectric constant that are too low (~55 instead of the reported 70). My dielectric constants are calculated from rather long trajectories (~2ns) and the values appear to be converged.

In your experience, which run parameters have the greatest influence on calculating the dielectric constant? Which run parameters are insignificant?

If you happen to have a set of input files that correctly reproduces the dielectric constant for water (any model will do), may I get it from you?

Thanks a lot!