Is it possible to isolate the Pauli Repulsion and London Dispersion terms in the simple Lennard Jones potential?

Hello,

With reference to the simple lj/cut potential style, I am wondering if it is possible in LAMMPS to separate the “12” and “6” terms. For example I would like to scale only the “6” London Dispersion term by a constant. Also I would like to access only the Pauli Repulsion term when defining my potentials. I would appreciate your assistance, thank you.

-Eric Bird

to have a repulsive-only interaction with the lj/cut pair style, you just need to define the cutoff at the minimum, i.e. at 2**(1/6)*sigma

it doesn’t make much sense to have different energies associated with the repulsive and attractive terms, since the shape of the repulsive term was chosen for computational efficiency, not for realism. if you want to have a more accurate representation of the repulsive term, you would need to look at using a morse potential or build a hybrid/overlay potential from using a zbl potential for the repulsive term with an ()**6 term taken from, e.g. pair style buck with A=0.

the only implementation having the LJ potential in A-B form is in pair style lennard/mdf which includes a switching function for forces and energies.

on top of all those considerations, there is always the option to tabulate potentials using pair style table (the recommended way to build them from within LAMMPS is via pair_style python and pair_write as that guarantees that the table file format is correct). tabulation requires careful testing and thus should first be done on a potential, that is available also analytically, e.g. with lj/cut to make certain that the choices for tabulation parameters and interpolation are producing sufficiently accurate results.

axel.