forked from lijiext/lammps
182 lines
7.6 KiB
Plaintext
182 lines
7.6 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_box command :h3
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[Syntax:]
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displace_box group-ID parameter args ... keyword value ... :pre
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group-ID = ID of group of atoms to displace :ulb,l
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one or more parameter/arg pairs may be appended :l
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parameter = {x} or {y} or {z} or {xy} or {xz} or {yz}
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{x}, {y}, {z} args = style value(s)
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style = {final} or {delta} or {scale} or {volume}
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{final} values = lo hi
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lo hi = box boundaries at end of run (distance units)
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{delta} values = dlo dhi
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dlo dhi = change in box boundaries at end of run (distance units)
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{scale} values = factor
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factor = multiplicative factor for change in box length at end of run
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{volume} value = none = adjust this dim to preserve volume of system
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{xy}, {xz}, {yz} args = style value
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style = {final} or {delta}
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{final} value = tilt
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tilt = tilt factor at end of run (distance units)
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{delta} value = dtilt
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dtilt = change in tilt factor at end of run (distance units) :pre
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zero or more keyword/value pairs may be appended :l
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keyword = {remap} or {units} :l
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{remap} value = {x} or {none}
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x = remap coords of atoms in group into deforming box
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none = no remapping of coords
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{units} value = {lattice} or {box}
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lattice = distances are defined in lattice units
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box = distances are defined in simulation box units :pre
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:ule
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[Examples:]
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displace_box all xy final -2.0 z final 0.0 5.0 units box
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displace_box all x scale 1.1 y volume z volume :pre
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[Description:]
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Change the volume and/or shape of the simulation box. Orthogonal
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simulation boxes have 3 adjustable parameters (x,y,z). Triclinic
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(non-orthogonal) simulation boxes have 6 adjustable parameters
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(x,y,z,xy,xz,yz). Any or all of them can be adjusted independently
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and simultaneously by this command. This fix can be used to expand or
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contract a box, or to apply a shear strain to a non-orthogonal box.
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Any parameter varied by this command must refer to a periodic
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dimension - see the "boundary"_boundary.html command. For parameters
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"xy", "xz", and "yz" this means both affected dimensions must be
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periodic, e.g. x and y for "xy". Dimensions not varied by this
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command can be periodic or non-periodic.
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The size and shape of the initial simulation box are specified by the
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"create_box"_create_box.html or "read_data"_read_data.html or
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"read_restart"_read_restart.html command used to setup the simulation,
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or they are the values from the end of the previous run. The
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"create_box"_create_box.html, "read data"_read_data.html, and
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"read_restart"_read_restart.html commands also determine whether the
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simulation box is orthogonal or triclinic and their doc pages explain
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the meaning of the xy,xz,yz tilt factors. If the displace_box command
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changes the xy,xz,yz tilt factors, then the simulation box must be
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triclinic, even if its initial tilt factors are 0.0.
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:line
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For the {x}, {y}, and {z} parameters, this is the meaning of their
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styles and values.
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For style {final}, the final lo and hi box boundaries of a dimension
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are specified. The values can be in lattice or box distance units.
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See the discussion of the units keyword below.
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For style {delta}, plus or minus changes in the lo/hi box boundaries
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of a dimension are specified. The values can be in lattice or box
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distance units. See the discussion of the units keyword below.
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For style {scale}, a multiplicative factor to apply to the box length
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of a dimension is specified. For example, if the initial box length
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is 10, and the factor is 1.1, then the final box length will be 11. A
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factor less than 1.0 means compression.
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The {volume} style changes the specified dimension in such a way that
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the box volume remains constant while other box dimensions are changed
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explicitly via the styles discussed above. For example, "x scale 1.1
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y scale 1.1 z volume" will shrink the z box length as the x,y box
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lengths increase, to keep the volume constant (product of x,y,z
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lengths). If "x scale 1.1 z volume" is specified and parameter {y} is
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unspecified, then the z box length will shrink as x increases to keep
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the product of x,z lengths constant. If "x scale 1.1 y volume z
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volume" is specified, then both the y,z box lengths will shrink as x
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increases to keep the volume constant (product of x,y,z lengths). In
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this case, the y,z box lengths shrink so as to keep their relative
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aspect ratio constant.
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For solids or liquids, note that when one dimension of the box is
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expanded by this command, it may be physically undesirable to hold the
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other 2 box lengths constant (unspecified by this command) since that
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implies a density change. Using the {volume} style for those 2
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dimensions to keep the box volume constant may make more physical
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sense, but may also not be correct for materials and potentials whose
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Poisson ratio is not 0.5.
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For the {scale} and {volume} styles, the box length is expanded or
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compressed around its mid point.
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:line
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For the {xy}, {xz}, and {yz} parameters, this is the meaning of their
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styles and values. Note that changing the tilt factors of a triclinic
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box does not change its volume.
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For style {final}, the final tilt factor is specified. The value
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can be in lattice or box distance units. See the discussion of the
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units keyword below.
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For style {delta}, a plus or minus change in the tilt factor is
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specified. The value can be in lattice or box distance units. See
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the discussion of the units keyword below.
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All of these styles change the xy, xz, yz tilt factors. In LAMMPS,
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tilt factors (xy,xz,yz) for triclinic boxes are always bounded by half
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the distance of the parallel box length. For example, if xlo = 2 and
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xhi = 12, then the x box length is 10 and the xy tilt factor must be
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between -5 and 5. Similarly, both xz and yz must be between
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-(xhi-xlo)/2 and +(yhi-ylo)/2. Note that this is not a limitation,
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since if the maximum tilt factor is 5 (as in this example), then
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configurations with tilt = ..., -15, -5, 5, 15, 25, ... are all
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equivalent. Any tilt factor specified by this command must be within
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these limits.
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:line
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The {remap} keyword determines whether atom positions are re-mapped to
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the new box. If {remap} is set to {x} (the default), atoms in the fix
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group are re-mapped; otherwise they are not. If {remap} is set to
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{none}, then this remapping does not take place.
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The {units} keyword determines the meaning of the distance units used
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to define various arguments. A {box} value selects standard distance
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units as defined by the "units"_units.html command, e.g. Angstroms for
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units = real or metal. A {lattice} value means the distance units are
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in lattice spacings. The "lattice"_lattice.html command must have
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been previously used to define the lattice spacing.
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:line
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The simulation box size or shape can be changed by arbitrarily large
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amounts by this command. This is not a problem, except that the
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mapping of processors to the simulation box is not changed by this
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command from its initial 3d configuration; see the
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"processors"_processors.html command. Thus, if the box size or shape
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changes dramatically, the simulation may not be as well load-balanced
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(atoms per processor) as the initial mapping tried to achieve.
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[Restrictions:]
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Any box dimension varied by this fix must be periodic.
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This command requires inter-processor communication to migrate atoms
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once they have moved. This means that your system must be ready to
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perform a simulation before using this command (force fields are
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setup, atom masses are set, etc).
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[Related commands:]
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"fix deform"_fix_deform.html
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[Default:]
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The option defaults are remap = x and units = lattice.
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