around the rotation axis and Rperp is a perpendicular vector from the

rotation axis to the atom.  If the defined

<A HREF = "atom_style.html">atom_style</A> assigns an angular velocity to each atom,

then each atom's angular velocity is also set to omega.

then each atom's angular velocity is also set to omega.  Note that the

direction of rotation for the atoms around the rotation axis is

consistent with the right-hand rule: if the right-hand's thumb points

along <I>R</I>, then the fingers wrap around in the direction of rotation.

</P>

<P>The <I>variable</I> style allows the position and velocity components of

each atom to be set by formulas specified via the

around the rotation axis and Rperp is a perpendicular vector from the

rotation axis to the atom.  If the defined

"atom_style"_atom_style.html assigns an angular velocity to each atom,

then each atom's angular velocity is also set to omega.

then each atom's angular velocity is also set to omega.  Note that the

direction of rotation for the atoms around the rotation axis is

consistent with the right-hand rule: if the right-hand's thumb points

along {R}, then the fingers wrap around in the direction of rotation.

The {variable} style allows the position and velocity components of

each atom to be set by formulas specified via the

either be primitive shapes (block, sphere, cylinder, etc) or

combinations of primitive shapes specified via the <I>union</I> or

<I>intersect</I> region styles.  These latter styles can be used to

construct particle containers with complex shapes.

construct particle containers with complex shapes.  Regions can also

change over time via keywords like <I>linear</I>, <I>wiggle</I>, and <I>rotate</I>,

which when used with this fix, have the effect of moving the region

surface in a prescribed manner.

</P>

<P>IMPORTANT NOTE: As discussed on the <A HREF = "region.html">region</A> command doc

page, regions in LAMMPS do not get wrapped across periodic boundaries.

either be primitive shapes (block, sphere, cylinder, etc) or

combinations of primitive shapes specified via the {union} or

{intersect} region styles.  These latter styles can be used to

construct particle containers with complex shapes.

construct particle containers with complex shapes.  Regions can also

change over time via keywords like {linear}, {wiggle}, and {rotate},

which when used with this fix, have the effect of moving the region

surface in a prescribed manner.

IMPORTANT NOTE: As discussed on the "region"_region.html command doc

page, regions in LAMMPS do not get wrapped across periodic boundaries.

</PRE>

<LI>zero or more keyword/value pairs may be appended 

<LI>keyword = <I>side</I> or <I>units</I> 

<LI>keyword = <I>side</I> or <I>units</I> or <I>vel</I> or <I>wiggle</I> or <I>rotate</I> 

<PRE>  <I>side</I> value = <I>in</I> or <I>out</I>

    <I>in</I> = the region is inside the specified geometry

  <I>units</I> value = <I>lattice</I> or <I>box</I>

    <I>lattice</I> = the geometry is defined in lattice units

    <I>box</I> = the geometry is defined in simulation box units

  <I>vel</I> args = Vx Vy Vz

    Vx,Vy,Vz = components of velocity vector (velocity units)

  <I>wiggle</I> args = Ax Ay Az period

    Ax,Ay,Az = components of amplitude vector (distance units)

    period = period of oscillation (time units)

  <I>rotate</I> args = Px Py Pz Rx Ry Rz period

    Px,Py,Pz = origin point of axis of rotation (distance units)

    Rx,Ry,Rz = axis of rotation vector

    period = period of rotation (time units) 

</PRE>

</UL>

region void cylinder y 2 3 5 -5.0 EDGE units box

region 1 prism 0 10 0 10 0 10 2 0 0

region outside union 4 side1 side2 side3 side4

region 2 sphere 0.0 0.0 0.0 5 side out wiggle 1 1 0 10 

</PRE>

<P>Note that the

direction of rotation for the atoms around the rotation axis is

consistent with the right-hand rule: if the right-hand's thumb points

along <I>R</I>, then the fingers wrap around in the direction of rotation.

</P>

<P><B>Description:</B>

</P>

<P>This command defines a geometric region of space.  Various other

Or the surface of the region can be used as a boundary wall via the

<A HREF = "fix_wall_region.html">fix wall/region</A> command.

</P>

<P>Normally, regions in LAMMPS are "static", meaning their geometric

extent does not change with time.  If the <I>vel</I> or <I>wiggle</I> or

<I>rotate</I> keyword is used, as described below, the region becomes

"dynamic", meaning it's location or orientation changes with time.

This may be useful, for example, when thermostatting a region, via the

compute temp/region command, or when the fix wall/region command uses

a region surface as a bounding wall on particle motion, i.e. a

rotating container.

</P>

<P>The lo/hi values for <I>block</I> or <I>cone</I> or <I>cylinder</I> or <I>prism</I> styles

can be specified as EDGE or INF.  EDGE means they extend all the way

to the global simulation box boundary.  Note that this is the current

listed regions combined.  The <I>intersect</I> style creates a region

consisting of the volume that is common to all the listed regions.

</P>

<HR>

<P>The <I>side</I> keyword determines whether the region is considered to be

inside or outside of the specified geometry.  Using this keyword in

conjunction with <I>union</I> and <I>intersect</I> regions, complex geometries

</P>

<P>The <I>units</I> keyword determines the meaning of the distance units used

to define the region for any argument above listed as having distance

units.  A <I>box</I> value selects standard distance units as defined by

the <A HREF = "units.html">units</A> command, e.g. Angstroms for units = real or

metal.  A <I>lattice</I> value means the distance units are in lattice

spacings.  The <A HREF = "lattice.html">lattice</A> command must have been

previously used to define the lattice spacings which are used as

follows:

units.  It also affects the scaling of the velocity vector specfied

with the <I>vel</I> keyword, the amplitude vector specified with the

<I>wiggle</I> keyword, and the rotation point specified with the <I>rotate</I>

keyword, since they each involve a distance metric.

</P>

<P>A <I>box</I> value selects standard distance units as defined by the

<A HREF = "units.html">units</A> command, e.g. Angstroms for units = real or metal.

A <I>lattice</I> value means the distance units are in lattice spacings.

The <A HREF = "lattice.html">lattice</A> command must have been previously used to

define the lattice spacings which are used as follows:

</P>

<UL><LI>For style <I>block</I>, the lattice spacing in dimension x is applied to

xlo and xhi, similarly the spacings in dimensions y,z are applied to

applied to the sphere center x,y,z.  The spacing in dimension x is

applied to the sphere radius. 

</UL>

<HR>

<P>If the <I>vel</I> or <I>wiggle</I> or <I>rotate</I> keywords are used, the region

is "dynamic", meaning its location or orientation changes with time.

No more than one of these keywords can be used at a time.  These

keywords cannot be used with a <I>union</I> or <I>intersect</I> style region.

Instead, the keywords should be used to define the individual

sub-regions of the <I>union</I> or <I>intersect</I> region.  Normally, each

sub-region should be "dynamic" in the same manner (e.g. rotate around

the same point), though this is not a requirement.

</P>

<P>The <I>vel</I> style moves the region at a constant velocity, so that its

position <I>X</I> = (x,y,z) as a function of time is given in vector

notation as

</P>

<PRE>X(t) = X0 + V * delta 

</PRE>

<P>where <I>X0</I> = (x0,y0,z0) is its position at the time the region is

specified, <I>V</I> is the specified velocity vector with components

(Vx,Vy,Vz), and <I>delta</I> is the time elapsed since the region was

specified. 

</P>

<P>The <I>wiggle</I> style moves the region in an oscillatory fashion, so that

its position <I>X</I> = (x,y,z) as a function of time is given in vector

notation as

</P>

<PRE>X(t) = X0 + A sin(omega*delta) 

</PRE>

<P>where <I>X0</I> = (x0,y0,z0) is its position at the time the region is

specified, <I>A</I> is the specified amplitude vector with components

(Ax,Ay,Az), <I>omega</I> is 2 PI / <I>period</I>, and <I>delta</I> is the time

elapsed since the region was specified.

</P>

<P>The <I>rotate</I> style rotates the region around a rotation axis <I>R</I> =

(Rx,Ry,Rz) that goes thru a point <I>P</I> = (Px,Py,Pz).  The <I>period</I> of

the rotation is also specified.  The direction of rotation for the

region around the rotation axis is consistent with the right-hand

rule: if your right-hand thumb points along <I>R</I>, then your fingers

wrap around the axis in the direction of rotation.

</P>

<P><B>Restrictions:</B>

</P>

<P>A prism cannot be of 0.0 thickness in any dimension; use a small z