forked from lijiext/lammps
99 lines
3.5 KiB
Plaintext
99 lines
3.5 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 wall/lj126 command :h3
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[Syntax:]
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fix ID group-ID wall/lj126 style coord epsilon sigma cutoff keyword values ... :pre
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ID, group-ID are documented in "fix"_fix.html command :ulb,l
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wall/lj126 = style name of this fix command :l
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style = {xlo} or {xhi} or {ylo} or {yhi} or {zlo} or {zhi} :l
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coord = position of wall :l
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epsilon = Lennard-Jones epsilon for wall-particle interaction :l
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sigma = Lennard-Jones sigma for wall-particle interaction :l
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cutoff = distance from wall at which wall-particle interaction is cut off (distance units) :l
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one or more keyword/value pairs may be appended :l
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keyword = {vel} :l
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{vel} args = v
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v = velocity of wall in perpendicular direction (velocity units) :pre
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:ule
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[Examples:]
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fix wallhi all wall/lj126 xhi 10.0 1.0 1.0 1.12
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fix leftwall all wall/lj126 zlo 0.0 1.0 1.0 0.858 vel 1.0 :pre
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[Description:]
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Bound the simulation domain on one of its faces with a Lennard-Jones
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wall that interacts with the atoms in the group. The energy E of
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wall-particle interactions is given by the 12-6 potential
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:c,image(Eqs/pair_lj.jpg)
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where {r} is the distance from the particle to the wall {coord}, and
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epsilon and sigma are the usual LJ parameters. Rc is the cutoff value
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specified in the command. This interaction provides a harder, more
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repulsive interaction with the wall than the softer 9-3 potential
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provided by the "fix wall/lj93"_fix_wall_lj93.html command.
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The wall potential is shifted so that the energy of a wall-particle
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interaction is 0.0 at the cutoff distance.
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If the {vel} keyword is specified, the position of wall will move
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during the simulation, based on its initial position (coord), the
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specified velocity (vel), and the time elapsed since the beginning of
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the simulation. {Xlo} or {xhi} walls move in the x direction with
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whatever sign you give the {v} argument. Ditto for {y} and {z} walls.
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See the note below about making the wall move continuously across
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multiple runs.
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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.
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The "fix_modify"_fix_modify.html {energy} option is supported by this
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fix to add the energy of interaction between atoms and the wall to the
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system's potential energy as part of "thermodynamic
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output"_thermo_style.html.
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This fix computes a scalar energy and a 3-vector of forces (on the
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wall), which can be accessed by various "output
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commands"_Section_howto.html#4_15. The scalar and vector values
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calculated by this fix are "extensive", meaning they scale with the
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number of atoms in the simulation.
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This fix can change the position of the wall, due to the {vel}
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keyword, continuously over multiple runs, using the {start} and {stop}
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keywords of the "run"_run.html command. If you do not do this, the
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wall position will be reset to {coord} at the beginning of each run.
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The forces due to this fix are imposed during an energy minimization,
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invoked by the "minimize"_minimize.html command.
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IMPORTANT NOTE: If you want the atom/wall interaction energy to be
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included in the total potential energy of the system (the quantity
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being minimized), you MUST enable the "fix_modify"_fix_modify.html
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{energy} option for this fix.
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[Restrictions:]
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Any dimension (xyz) that has a LJ 12/6 wall must be non-periodic.
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[Related commands:]
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"fix wall/reflect"_fix_wall_reflect.html, "fix
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wall/lj93"_fix_wall_lj93.html
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[Default:]
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The option defaults are vel = 0.
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