(no subject)

I'm doing a simulation in which different pressures and densities are
used as inputs and outputs,in order. In low pressures, the densities
where compatible with experimental data whereas by increasing the
pressures they were not compatible anymore. In all pressures, the
cutoffs were the same. Since by increasing the cutoff at the pressure
of 102 atm which is the highest one, the density increased; I want to
know whether I should reduce the cutoffs by increasing the pressure or
not?

That’s a question for your model, not for LAMMPS.
You can change the density by changing your input
(size of simulation box and number of particles),
and you can control the pressure via fix npt.
Those are all input parameters that you need
to choose.

Steve