Dear LAMMPS users,
I am having some trouble understanding how (or if) LAMMPS ensures that the force is continuous when using lj/cut/tip4p/long with the pppm/tip4p solver.
Should I include the pair_modify shift yes to make sure the LJ force between the oxygen atoms is continuous, and then assume that the combination of the particle-particle and the particle-mesh contributions to the Coulomb part of the force is continuous?
Best regards
Bjørn
Dear LAMMPS users,
I am having some trouble understanding how (or if) LAMMPS ensures that the
force is continuous when using lj/cut/tip4p/long with the pppm/tip4p solver.Should I include the pair_modify shift yes to make sure the LJ force
between the oxygen atoms is continuous, and then assume that the
combination of the particle-particle and the particle-mesh contributions to
the Coulomb part of the force is continuous?
pair_modify shift does *not* affect the force, it only shifts the entire
potential.
the discontinuity due to the truncation of the LJ components (primarily the
r**6 term) is very small, provided your cutoff is sufficiently large (~12
\AA and beyond), and it is usually neglected.
if you need more accurate pressure, you can use pair_modify tail yes, to
compute an average correction of the tail that is being cut off.
if you want to use a shorter cutoff and still have accurate evaluation of
the LJ (r**6) part, you can use pair style lj/long/tip4p/long in
combination with pppm/disp/tip4p.
axel.