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lammps/doc/region.txt
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"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)
:line
region command :h3
[Syntax:]
region ID style args keyword value ... :pre
ID = user-assigned name for the region :ulb,l
style = {block} or {cylinder} or {prism} or {sphere} or {union} or {intersect} :l
{block} args = xlo xhi ylo yhi zlo zhi
xlo,xhi,ylo,yhi,zlo,zhi = bounds of block in all
dimensions (distance units)
{cylinder} args = dim c1 c2 radius lo hi
dim = {x} or {y} or {z} = axis of cylinder
c1,c2 = coords of cylinder axis in other 2 dimensions (distance units)
radius = cylinder radius (distance units)
lo,hi = bounds of cylinder in dim (distance units)
{prism} args = xlo xhi ylo yhi zlo zhi xy xz yz
xlo,xhi,ylo,yhi,zlo,zhi = bounds of untilted prism (distance units)
xy = distance to tilt y in x direction (distance units)
xz = distance to tilt z in x direction (distance units)
yz = distance to tilt z in y direction (distance units)
{sphere} args = x y z radius
x,y,z = center of sphere (distance units)
radius = radius of sphere (distance units)
{union} args = N reg-ID1 reg-ID2 ...
N = # of regions to follow, must be 2 or greater
reg-ID1,reg-ID2, ... = IDs of regions to join together
{intersect} args = N reg-ID1 reg-ID2 ...
N = # of regions to follow, must be 2 or greater
reg-ID1,reg-ID2, ... = IDs of regions to intersect :pre
zero or more keyword/value pairs may be appended to the args :l
keyword = {side} or {units} :l
{side} value = {in} or {out}
{in} = the region is inside the specified geometry
{out} = the region is outside the specified geometry
{units} value = {lattice} or {box}
{lattice} = the geometry is defined in lattice units
{box} = the geometry is defined in simulation box units :pre
:ule
[Examples:]
region 1 block -3.0 5.0 INF 10.0 INF INF
region 2 sphere 0.0 0.0 0.0 5 side out
region void cylinder y 2 3 5 -5.0 INF units box
region 1 prism 0 10 0 10 0 10 2 0 0
region outside union 4 side1 side2 side3 side4 :pre
[Description:]
This command defines a geometric region of space. Various other
commands use regions. For example, the region can be filled with
atoms via the "create_atoms"_create_atoms.html command. Or the atoms
in the region can be identified as a group via the "group"_group.html
command, or deleted via the "delete_atoms"_delete_atoms.html command.
The lo/hi values for {block} or {cylinder} or {prism} styles can be
specified as INF which means they extend all the way to the global
simulation box boundary. If a region is defined before the simulation
box has been created (via "create_box"_create_box.html or
"read_data"_read_data.html or "read_restart"_read_restart.html
commands), then an INF parameter cannot be used.
For style {cylinder}, the c1,c2 params are coordinates in the 2 other
dimensions besides the cylinder axis dimension. For dim = x, c1/c2 =
y/z; for dim = y, c1/c2 = x/z; for dim = z, c1/c2 = x/y. Thus the
third example above specifes a cylinder with its axis in the
y-direction located at x = 2.0 and z = 3.0, with a radius of 5.0, and
extending in the y-direction from -5.0 to the upper box boundary.
For style {prism}, a parallelepiped is defined (it's too hard to spell
parallelepiped in an input script!). Think of the parallelepided as
initially an axis-aligned orthogonal box with the same xyz lo/hi
parameters as region style {block} would define. Then, while holding
the (xlo,ylo,zlo) corner point fixed, the box is "skewed" or "tilted"
in 3 directions. First, for the lower xy face of the box, the {xy}
factor is how far the upper y edge is shifted in the x direction. The
lower xy face is now a parallelogram. A plus or minus value for {xy}
can be specified; 0.0 means no tilt. Then, the upper xy face of the
box is translated in the x and y directions by {xz} and {yz}. This
results in a parallelepiped whose "origin" is at (xlo,ylo,zlo) with 3
edge vectors starting from its origin given by a = (xhi-xlo,0,0); b =
(xy,yhi-ylo,0); c = (xz,yz,zhi-zlo).
A prism region used with the "create_box"_create_box.html command must
have tilt factors (xy,xz,yz) that do not skew the box more than half
the distance of the parallel box length. For example, if xlo = 2 and
xhi = 12, then the x box length is 10 and the xy tilt factor must be
between -5 and 5. Similarly, both xz and yz must be between
-(xhi-xlo)/2 and +(yhi-ylo)/2. Note that this is not a limitation,
since if the maximum tilt factor is 5 (as in this example), then
configurations with tilt = ..., -15, -5, 5, 15, 25, ... are all
equivalent.
The {union} style creates a region consisting of the volume of all the
listed regions combined. The {intesect} style creates a region
consisting of the volume that is common to all the listed regions.
The {side} keyword determines whether the region is considered to be
inside or outside of the specified geometry. Using this keyword in
conjunction with {union} and {intersect} regions, complex geometries
can be built up. For example, if the interior of two spheres were
each defined as regions, and a {union} style with {side} = out was
constructed listing the region-IDs of the 2 spheres, the resulting
region would be all the volume in the simulation box that was outside
both of the spheres.
The {units} keyword determines the meaning of the distance units used
to define the region. A {box} value selects standard distance units
as defined by the "units"_units.html command, e.g. Angstroms for units
= real or metal. A {lattice} value means the distance units are in
lattice spacings. The "lattice"_lattice.html command must have been
previously used to define the lattice spacing.
[Restrictions:]
A prism cannot be of 0.0 thickness in any dimension; use a small z
thickness for 2d simulations. For 2d simulations, the xz and yz
parameters must be 0.0.
[Related commands:]
"lattice"_lattice.html, "create_atoms"_create_atoms.html,
"delete_atoms"_delete_atoms.html, "group"_group.html
[Default:]
The option defaults are side = in and units = lattice.
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