Dear lammps developers,
I have checked the manual, but I am still confused about "tip4p" command and how to build tip4p water model. My system includes water and ions (such as Na+). My questions are as follows.
1) build tip4p water model
From the mailing list, I find that someone use parameters of tip4p water to build a three sites water model to represent the tip4p water model, and there is no mention of M site in the data file, what's more, the charge of oxygen is assigned to O atom directly. In the input file, "pair_style lj/cut/tip4p/long" command is used to call tip4p water model.
Question: I am wondering whether this is a right process to build the tip4p water model since the M site possesses the charge of oxygen and is massless in tip4p water model.
2) Interactions between water and ions
I plan to use "pair_style lj/cut/tip4p/long" to calculate the interactions of O and H atoms in tip4p water model, and use "lj/cut/coul/long" to calculate the interactions of Na.
Question: for interactions between O and Na, if I want to calculate LJ and coulombic potentials, do I still need to mention "tip4p" in the pair_style command? Which one should I use, "lj/cut/tip4p/long" or "lj/cut/coul/long"?
3) I have seen that the LJ epsilon and sigma of H-H, O-H are 0.0.
Question: does this mean we only need to consider O atom for LJ in tip4p water when calculating the LJ interactions between water and other molecules, without consideing LJ of H atom?
4) Since the charge of oxygen is placed on M site, while calculating the coulombic interactions between O and Na, do we still think oxygen charge is on O atom and use the O atom type to calculate the coulombic interaction? such as "pair_coeff O_type Na_type .........." or "pair_coeff M_type Na_type ......."
Best wishes
Xiaohui She
University of Wisconsin-Madison