forked from lijiext/lammps
79 lines
3.0 KiB
Plaintext
79 lines
3.0 KiB
Plaintext
"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
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:link(lws,http://lammps.sandia.gov)
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:link(ld,Manual.html)
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:link(lc,Section_commands.html#comm)
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:line
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fix nve/limit command :h3
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[Syntax:]
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fix ID group-ID nve/limit xmax :pre
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ID, group-ID are documented in "fix"_fix.html command
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nve = style name of this fix command
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xmax = maximum distance an atom can move in one timestep (distance units) :ul
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[Examples:]
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fix 1 all nve/limit 0.1 :pre
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[Description:]
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Perform constant NVE updates of position and velocity for atoms in the
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group each timestep. A limit is imposed on the maximum distance an
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atom can move in one timestep. This is useful when starting a
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simulation with a configuration containing highly overlapped atoms.
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Normally this would generate huge forces which would blow atoms out of
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the simulation box, causing LAMMPS to stop with an error.
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Using this fix can overcome that problem. Forces on atoms must still
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be computable (which typically means 2 atoms must have a separation
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distance > 0.0). But large velocities generated by large forces are
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reset to a value that corresponds to a displacement of length {xmax}
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in a single timestep. {Xmax} is specified in distance units; see the
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"units"_units.html command for details. The value of {xmax} should be
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consistent with the neighbor skin distance and the frequency of
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neighbor list re-building, so that pairwise interactions are not
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missed on successive timesteps as atoms move. See the
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"neighbor"_neighbor.html and "neigh_modify"_neigh_modify.html commands
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for details.
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Note that if a velocity reset occurs the integrator will not conserve
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energy. On steps where no velocity resets occur, this integrator is
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exactly like the "fix nve"_fix_nve.html command. Since forces are
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unaltered, pressures computed by thermodynamic output will still be
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very large for overlapped configurations.
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[Restart, fix_modify, output, run start/stop, minimize info:]
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No information about this fix is written to "binary restart
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files"_restart.html. None of the "fix_modify"_fix_modify.html options
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are relevant to this fix.
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This fix computes a scalar quantity which is the count of how many
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updates of atom's velocity/position were limited by the maximum
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distance criterion. This should be roughly the number of atoms so
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affected, except that updates occur at both the beginning and end of a
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timestep in a velocity Verlet timestepping algorithm. This is a
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cumulative quantity for the current run, but is re-initialized to
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zero each time a run is performed. This value can be accessed by
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various "output commands"_Section_howto.html#4_15. The scalar value
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calculated by this fix is "extensive", meaning it scales with the
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number of atoms in the simulation.
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No parameter of this fix can be used with the {start/stop} keywords of
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the "run"_run.html command. This fix is not invoked during "energy
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minimization"_minimize.html.
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[Restrictions:] none
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[Related commands:]
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"fix nve"_fix_nve.html, "fix nve/noforce"_fix_nve_noforce.html,
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"pair_style soft"_pair_soft.html
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[Default:] none
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