What would be best water model to simulate moist N2?

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There are several models available to simulate water (e.g., http://www1.lsbu.ac.uk/water/water_models.html). Most of them are developed/targeted to simulate pure liquid water. However, in a situation like moist N2, most of the collisions of a water molecule happen with nitrogen molecules. My question is - which water model (or better, I should call it as model for N2 - H2O interaction) would be best suitable to model these intermolecular interactions?

One possible way out (as done in most of the available literature) is to use SPC/E or TIP4P model and then apply the Lorentz–Berthelot mixing rule to get interaction parameters (sigma and epsilon) to model intermolecular interaction between N2 and H2O. The problem with the use of such a mixing rule to simulate a collision between H2O and N2 molecule is this— Most of the water-models use a combination of coulombic and LJ interaction to simulate ‘water - water’ interaction. Point electric charges are placed on three sites (on each atom), and one LJ site (Lennard-Jones potential) is placed at/near oxygen atom.

N2 is a nonpolar and poorly polarizable molecule and is usually modeled with an LJ potential. No charge is placed on any N atoms. During a collision between N2 and H2O molecule, the N atom (of the N2 molecule) can interact with both the hydrogen and oxygen atoms (from H2O molecule). However, if we apply a mixing rule between the LJ potential of N2 and that place on O atom of H2O, we will be modeling only the O and N interaction and ignoring the H and N interaction. It does not seem ok, especially if the rotational energy exchange is our primary concern.

So, to properly simulate an N2 and H2O collision, we need an interaction model that takes into account interaction between the N and O as well as N and H. Do there exist any such model? Or any other suitable approximation?

Thanks in advance. Especially to Axel and Steve for the time and efforts they put into sharing their invaluable expertise with everyone. Your previous answers in the mailing list has benefitted students like me a lot. I don’t think I’ll ever be able to thank you enough.

Thanks again. and sorry for a long post.

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I can’t say anything about “the best”, and - frankly - this is a question about your science and not about LAMMPS, so it would be considered somewhat off-topic for this list. It also is something that is best answered through a careful survey of the published literature.

But it just so happened, that I did some simulations of low density supercritical water when I was an undergraduate. For those studies we used the BJH (Bopp-Jancso-Heinzinger) water model, Chemical Physics Letters, 98(2), 129-133. This was with an in-house MD code, so I don’t know if LAMMPS has the necessary potential functions. But regardless of that, this should give you a hint what to look up in the literature, as later papers using water in gas phase have a non-zero probability of citing this paper, so it could help to figure out what is state of the art in the field.

Axel.