Is it possible to set different pair_modify options (e.g. tail, or shift) to different logical values for different pair styles

LAMMPS LAMMPS General Discussion
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1

Dear all,

I want to use two separate pair styles of lj type, in which I want to truncate one of the pair styles and not add the tail corrections, but for the other I require to add the tail correction as well. But the documentation for pair styles say that if a new pair style is introduced it will over write the pair_modify settings.

Is there some way I can implement what I want?

Regards,
Chaitanya

2

I don’t think so. The two options exclude each other.

3

Hello Axel,

I think you understood the question such that I am wanting to use tail and shift options at once. But to clarify, that is not the case. I tried to ask the question in a general sense and hence I think created the confusion.

I just want to use tail as yes for one pair style: lj/cut/tip4p/long and no for another pair style: lj/cut.

Is doing so possible?

Chaitanya

4

No. It would be unphysical, too, and it makes no sense, even if you would find a hack around the limitations in LAMMPS. I most certainly will not intentionally give advice to people that will lead to bogus simulation results. You don’t seem to understand what the tail correction does. It is probably not very useful for your system in the first place. But since you share no specifics, nobody can tell.

You have been asking similarly conceptually flawed questions about Coulomb interactions in the past, this is not so different. Only that the tail correction is more approximate and assumes a homogeneous system.

5

Thank you for the reply Axel.

Although it seems to be un-physical, it is not that I am trying to generate bogus simulation results. Just that I am simultaneously also using a theory to calculate the properties, I need to generate some trajectories with a certain hamiltonian which I am trying to get using these hacks as you called it.

Thanks, and regards,
Chaitanya

6

You could emulate the LJ/cut potential using pair styles like table, python or lepton, which are too generic to have tail corrections implemented. I hope you know exactly what you are looking for, because this is a very non-standard setup.

7

Thanks for the suggestions. I will look into it and see if it is helpful.