Hi Ave,
This is a very hard problem you have been asked to do, especially at an undergraduate level. In particular, most three- and four-point water models do not model ice well. Most of them show freezing points of -30°C – here is a recent paper that discusses this: https://pubs.acs.org/doi/10.1021/acsomega.0c02638
Let me counter-propose a reasonable undergraduate research project. Earlier this year, a great molecular dynamics model for monovalent alkali-metal and halide ions was released: Force field for halide and alkali ions in water based on single-ion and ion-pair thermodynamic properties for a wide range of concentrations | The Journal of Chemical Physics | AIP Publishing
However, the authors validated this model for SPC/E water in GROMACS. In materials modelling many scientists use LAMMPS, and I personally tend to use the newer OPC family of water models where I can: Accuracy limit of rigid 3-point water models | The Journal of Chemical Physics | AIP Publishing .
Now, it is very likely that the ion models I mentioned earlier will show similar performance in OPC3 water in LAMMPS as with SPC/E water in GROMACS. But it would be nice if someone explicitly showed it. That someone can be you:
- Generate simulations for the ions in SPC/E water in LAMMPS to match the GROMACS simulations and confirm that you get similar results.
- Replace the SPC/E water with OPC3 water and see whether it makes a difference or not.
This would be a reasonable undergraduate project: setting up simulations of a homogeneous phase under barostatting and thermostatting and choosing variables (continuous ones being the sale concentration, and discontinuous ones such as the choice of force field and software) against which differences can be quantified and rationalised.
By the way, this is how I like to do science: find a meaningful problem (whether different softwares return similar results, which they should, and whether different water models behave similarly, which they should but there will certainly be small differences), and where either a “positive” or a “negative” result would be interesting and would have some explanation that fits in with the wider literature.