Hello.
I simulate liquid organic salts with OPLS-AA, there are 50k atoms in the system. During equilibration I use minimize command as one of first steps. Minimization changes system’s energy dramatically from +e12 to -e15, mostly because Coulomb energy is changing at the same range. The resulting system is unstable(max force e29) and I use several other steps to equilibrate it and at the end I have system with total energy +e5, both for TotEng and Ecoul, force max ~100. This equilibrated system is stable, used later without problems and looks like correct.
Whole system is charge neutral at any step, triclinic periodic. I use “pair_style hybrid lj/cut/coul/long 10.0 10.0”
What could be the reason that minimize converges to such a low energy state? Why system after minimization has huge forces?
Thanks
–Best wishes,
Boris Zimka
Hello.
I simulate liquid organic salts with OPLS-AA, there are 50k atoms in the
system. During equilibration I use minimize command as one of first
steps. Minimization changes system's energy dramatically from +e12 to -e15,
mostly because Coulomb energy is changing at the same range. The resulting
system is unstable(max force e29) and I use several other steps to
equilibrate it and at the end I have system with total energy +e5, both
for TotEng and Ecoul, force max ~100. This equilibrated system is stable,
used later without problems and looks like correct.
Whole system is charge neutral at any step, triclinic periodic. I use
"pair_style hybrid lj/cut/coul/long 10.0 10.0"
What could be the reason that minimize converges to such a low energy
state? Why system after minimization has huge forces?
hard to say without actually seeing the geometries, inputs and making some
tests. most likely, you have some very close contacts or unphysical
geometry in your initial configuration. minimization will take you to the
next minimum, which may not be the global minimum. particularly with bad
initial geometries you may get trapped in some metastable configuration.
axel.