Dear Lammps users and developers,
I’m writing to ask about the possibility of using the flexible q-TIP4p/f water model developed by Habershon et al. in which the position of the negative charge (i.e. qdist in lj/cut/coul/long is a function of the position of hydrogen and oxygen atoms. To the best of my knowledge, it needs modifying the lammps source code. However, before starting to do so I was wondering if anyone already has done it or if there can be any shortcut method to do so in LAMMPS.
what makes this TIP4P variant different from the ones that are already supported in LAMMPS?
the TIP4P coulomb code in LAMMPS is quite sophisticated and it took significant effort to make it work reliably, so it is not an easy task to modify it.
Thanks Axel for the response.
As you might know, One of the reason of developing these flexible TIP4P potentials was to be able to mimic vaibrational mode. In these models, the position of negative charge (qdist) is variant w.r.t. the position of other atoms. However, I saw on the internet that some people use qdist = 0.1546 which I doubt about using it as a constant based on the content of the paper . This constant qdist should be correct only when the atoms in a molecule lie in their ideal position. Thus, it changes during a dynamic simulation. I attached the formula and the Author’s explanation from the paper here.
Please note that people reference to  as TIP4P/f and to Habershon et al. work as q- TIP4P/f in the literature.
 González, M. A., & Abascal, J. L. (2011). A flexible model for water based on TIP4P/2005. The Journal of chemical physics, 135(22), 224516.