Cutoff issue buckingham coulombic potential in LAMMPS

[sogol]

Kspace ewald (coul/long potential) generates strange forces

You are only turning off the Lennard-Jones interactions. You still have Coulomb interactions and atoms with charges and thus there should be forces due to the charges from the Kspace style. That one always computes interactions between all atoms in the system. It is not a pair-wise computation, so how you assign pair styles in the hybrid pair style is irrelevant. This can be easily confirmed by changing your thermo_style command to: thermo_style custom step etotal epair evdwl ecoul elong W…

Here is the link I am talking about.