I am currently trying to simulate a large box of QM/MM water molecules with SPC/Fw model and GGA DFT functional (a cube of 40 angstrom sides). To validate the QM and MM simulations separately, I am testing a pure MM box of same dimensions with SPC/Fw model, and I was trying to set the LJ and coulomb cutoff length. I am using CP2K software and pairwise-style cutoff. By the conventions I should set the cutoff to <1/2 of smallest box dimension (~19 angstroms). But I encountered these two papers about this issue for liquid water:
both published in 2006, which suggests that larger cutoff lengths can lead to "layering" and other artifacts in pure water simulations. Elsewhere, I can find papers which suggest to keep the cutoff length to 9-12 angstroms (as discussed here: Rule-of-thumb for Morse potential cutoff in molecular dynamics?). So my question is: Does it makes sense then to limit cutoffs till 12 angstroms? And are there any significant issues particularly for QM/MM simulations?
For more details on the QM/MM setup: I am using an additive QM/MM system with electrostatic embedding.