forked from lijiext/lammps
94 lines
3.8 KiB
Plaintext
94 lines
3.8 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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create_box command :h3
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[Syntax:]
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create_box N region-ID :pre
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N = # of atom types to use in this simulation
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region-ID = ID of region to use as simulation domain :ul
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[Examples:]
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create_box 2 mybox :pre
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[Description:]
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This command creates a simulation box based on the specified region.
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Thus a "region"_region.html command must first be used to define a
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geometric domain.
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The argument N is the number of atom types that will be used in the
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simulation.
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If the region is not of style {prism}, then LAMMPS encloses the region
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(block, sphere, etc) with an axis-aligned orthogonal bounding box
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which becomes the simulation domain.
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If the region is of style {prism}, LAMMPS creates a non-orthogonal
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simulation domain shaped as a parallelepiped with triclinic symmetry.
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As defined by the "region prism"_region.html command, the
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parallelepiped has its "origin" at (xlo,ylo,zlo) and is defined by 3
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edge vectors starting from the origin given by A = (xhi-xlo,0,0); B =
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(xy,yhi-ylo,0); C = (xz,yz,zhi-zlo). {Xy,xz,yz} can be 0.0 or
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positive or negative values and are called "tilt factors" because they
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are the amount of displacement applied to faces of an originally
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orthogonal box to transform it into the parallelipiped.
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A {prism} region used with the create_box command must have tilt
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factors (xy,xz,yz) that do not skew the box more than half the
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distance of the parallel box length. For example, if xlo = 2 and xhi
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= 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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geometrically equivalent.
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See "Section_howto 12"_Section_howto.html#howto_12 of the doc pages
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for a geometric description of triclinic boxes, as defined by LAMMPS,
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and how to transform these parameters to and from other commonly used
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triclinic representations.
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When a prism region is used, the simulation domain must be periodic in
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any dimensions with a non-zero tilt factor, as defined by the
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"boundary"_boundary.html command. I.e. if the xy tilt factor is
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non-zero, then both the x and y dimensions must be periodic.
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Similarly, x and z must be periodic if xz is non-zero and y and z must
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be periodic if yz is non-zero. Also note that if your simulation will
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tilt the box, e.g. via the "fix deform"_fix_deform.html command, the
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simulation box must be defined as triclinic, even if the tilt factors
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are initially 0.0.
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IMPORTANT NOTE: If the system is non-periodic (in a dimension), then
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you should not make the lo/hi box dimensions (as defined in your
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"region"_region.html command) radically smaller/larger than the extent
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of the atoms you eventually plan to create, e.g. via the
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"create_atoms"_create_atoms.html command. For example, if your atoms
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extend from 0 to 50, you should not specify the box bounds as -10000
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and 10000. This is because LAMMPS uses the specified box size to
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layout the 3d grid of processors. A huge (mostly empty) box will be
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sub-optimal for performance when using "fixed" boundary conditions
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(see the "boundary"_boundary.html command). When using "shrink-wrap"
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boundary conditions (see the "boundary"_boundary.html command), a huge
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(mostly empty) box may cause a parallel simulation to lose atoms the
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first time that LAMMPS shrink-wraps the box around the atoms.
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[Restrictions:]
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An "atom_style"_atom_style.html and "region"_region.html must have
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been previously defined to use this command.
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[Related commands:]
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"create_atoms"_create_atoms.html, "region"_region.html
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[Default:] none
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