ring force, large frequency -&gt; small mass -&gt; rapid fluctations
for nose/hoover style, units of frequency/damping constant are
  inverse time, so a value of 0.001 means relax in a timespan on the 
  order of 1000 fmsec (real units) or 1000 tau (LJ units)
IMPORTANT NOTE: the computation of P in LAMMPS does not include
  a long-range Van der Waals correction, this introduces a known
  error when performing constant P simulations since the correction
  factor changes as the box size varies

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