Point charge without LJ coefficient

Dear Lammps users,

I am trying to run a simulation with the TraPPE 10 sites Toluene and TIP4P water model.
The toluene has 3 point charges which are not located on atoms sites.

I am using lj/long/tip4p/long pairstyle wit very small epsilon and sigma (10E-10 to 10E-16) for the point charges, but even then, there is always a moment when my positive charge from the water’s hydrogen is attracted by my negative toluene’s point charge and they end overlapping resulting in a simulation crash.

I would like to know if there is a way to put sigma and epsilon to 0 or to turn off the lennard-jones interraction only for these specific atoms.

Thank you in advance for your help.

Dear Lammps users,

I am trying to run a simulation with the TraPPE 10 sites Toluene and TIP4P water model.
The toluene has 3 point charges which are not located on atoms sites.

I am using lj/long/tip4p/long pairstyle wit very small epsilon and sigma (10E-10 to 10E-16) for the point charges, but even then, there is always a moment when my positive charge from the water’s hydrogen is attracted by my negative toluene’s point charge and they end overlapping resulting in a simulation crash.

I would like to know if there is a way to put sigma and epsilon to 0 or to turn off the lennard-jones interraction only for these specific atoms.

the crash is due to the coulomb interactions not the LJ interactions. if those atoms get too close, then there is something wrong with your model. setting epsilon to 0.0 (but keeping sigma at “normal” values, as you may run into problems with division by zero or overflows otherwise with certain settings) is turning off LJ interactions completely. if you look at the formulation of the LJ potential, this should be obvious.

you are not providing enough information to determine what else is wrong in your model. has the toluene model you are using parameterized for interaction with TIP4P water?

axel.