forked from lijiext/lammps
98 lines
3.6 KiB
Plaintext
98 lines
3.6 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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displace_atoms command :h3
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[Syntax:]
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displace_atoms group-ID style args keyword value ... :pre
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group-ID = ID of group of atoms to displace :ulb,l
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style = {move} or {ramp} or {random} :l
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{move} args = delx dely delz
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delx,dely,delz = distance to displace in each dimension (distance units)
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{ramp} args = ddim dlo dhi dim clo chi
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ddim = {x} or {y} or {z}
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dlo,dhi = displacement distance between dlo and dhi (distance units)
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dim = {x} or {y} or {z}
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clo,chi = lower and upper bound of domain to displace (distance units)
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{random} args = dx dy dz seed
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dx,dy,dz = random displacement magnitude in each dimension (distance units)
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seed = random # seed (positive integer) :pre
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zero or more keyword/value pairs may be appended :l
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keyword = {units}
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value = {box} or {lattice} :pre
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:ule
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[Examples:]
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displace_atoms top move 0 -5 0 units box
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displace_atoms flow ramp x 0.0 5.0 y 2.0 20.5 :pre
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[Description:]
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Displace a group of atoms. This can be used to move atoms a large
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distance before beginning a simulation or to randomize atoms initially
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on a lattice. For example, in a shear simulation, an initial strain
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can be imposed on the system. Or two groups of atoms can be brought
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into closer proximity.
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The {move} style displaces the group of atoms by the specified 3d
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distance.
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The {ramp} style displaces atoms a variable amount in one dimension
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depending on the atom's coordinate in a (possibly) different
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dimension. For example, the second example command displaces atoms in
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the x-direction an amount between 0.0 and 5.0 distance units. Each
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atom's displacement depends on the fractional distance its y
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coordinate is between 2.0 and 20.5. Atoms with y-coordinates outside
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those bounds will be moved the minimum (0.0) or maximum (5.0) amount.
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The {random} style independently moves each atom in the group by a
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random displacement, uniformly sampled from a value between -dx and
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+dx in the x dimension, and similarly for y and z. Random numbers are
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used in such a way that the displacement of a particular atom is the
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same, regardless of how many processors are being used.
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Distance units for displacement are determined by the setting of {box}
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or {lattice} for the {units} keyword. {Box} means distance units as
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defined by the "units"_units.html command - e.g. Angstroms for {real}
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units. {Lattice} means distance units are in lattice spacings. The
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"lattice"_lattice.html command must have been previously used to
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define the lattice spacing.
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:line
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Care should be taken not to move atoms on top of other atoms. After
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the move, atoms are remapped into the periodic simulation box if
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needed.
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Atoms can be moved arbitrarily long distances by this command. If the
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simulation box is non-periodic, this can change its size or shape.
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This is not a problem, except that the mapping of processors to the
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simulation box is not changed by this command from its initial 3d
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configuration; see the "processors"_processors.html command. Thus, if
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the box size or shape changes dramatically, the simulation may not be
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as well load-balanced (atoms per processor) as the initial mapping
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tried to achieve.
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[Restrictions:]
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This command requires inter-processor communication to migrate atoms
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once they have been displaced. This means that your system must be
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ready to perform a simulation before using this command (force fields
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are setup, atom masses are set, etc).
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[Related commands:]
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"lattice"_lattice.html
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[Default:]
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The option defaults are units = lattice.
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