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<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A>
</CENTER>
<HR>
<H3>compute property/atom command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>compute ID group-ID property/atom input1 input2 ...
</PRE>
<UL><LI>ID, group-ID are documented in <A HREF = "compute.html">compute</A> command
<LI>property/atom = style name of this compute command
<LI>input = one or more atom attributes
<PRE> possible attributes = id, mol, proc, type, mass,
x, y, z, xs, ys, zs, xu, yu, zu, ix, iy, iz,
vx, vy, vz, fx, fy, fz,
q, mux, muy, muz, mu,
radius, diameter, omegax, omegay, omegaz,
angmomx, angmomy, angmomz,
shapex,shapey, shapez,
quatw, quati, quatj, quatk, tqx, tqy, tqz,
end1x, end1y, end1z, end2x, end2y, end2z,
corner1x, corner1y, corner1z,
corner2x, corner2y, corner2z,
corner3x, corner3y, corner3z,
nbonds,
vfrac, s0,
spin, eradius, ervel, erforce,
rho, drho, e, de, cv,
i_name, d_name
</PRE>
<PRE> id = atom ID
mol = molecule ID
proc = ID of processor that owns atom
type = atom type
mass = atom mass
x,y,z = unscaled atom coordinates
xs,ys,zs = scaled atom coordinates
xu,yu,zu = unwrapped atom coordinates
ix,iy,iz = box image that the atom is in
vx,vy,vz = atom velocities
fx,fy,fz = forces on atoms
q = atom charge
mux,muy,muz = orientation of dipole moment of atom
mu = magnitude of dipole moment of atom
radius,diameter = radius,diameter of spherical particle
omegax,omegay,omegaz = angular velocity of spherical particle
angmomx,angmomy,angmomz = angular momentum of aspherical particle
shapex,shapey,shapez = 3 diameters of aspherical particle
quatw,quati,quatj,quatk = quaternion components for aspherical or body particles
tqx,tqy,tqz = torque on finite-size particles
end12x, end12y, end12z = end points of line segment
corner123x, corner123y, corner123z = corner points of triangle
nbonds = number of bonds assigned to an atom
</PRE>
<PRE> PERI package per-atom properties:
vfrac = ???
s0 = ???
</PRE>
<PRE> USER-EFF and USER-AWPMD package per-atom properties:
spin = electron spin
eradius = electron radius
ervel = electron radial velocity
erforce = electron radial force
</PRE>
<PRE> USER-SPH package per-atom properties:
rho = ???
drho = ???
e = ???
de = ???
cv = ???
</PRE>
<PRE> <A HREF = "fix_property_atom.html">fix property/atom</A> per-atom properties:
i_name = custom integer vector with name
d_name = custom integer vector with name
</PRE>
</UL>
<P><B>Examples:</B>
</P>
<PRE>compute 1 all property/atom xs vx fx mux
compute 2 all property/atom type
compute 1 all property/atom ix iy iz
</PRE>
<P><B>Description:</B>
</P>
<P>Define a computation that simply stores atom attributes for each atom
in the group. This is useful so that the values can be used by other
<A HREF = "Section_howto.html#howto_15">output commands</A> that take computes as
inputs. See for example, the <A HREF = "compute_reduce.html">compute reduce</A>,
<A HREF = "fix_ave_atom.html">fix ave/atom</A>, <A HREF = "fix_ave_histo.html">fix ave/histo</A>,
<A HREF = "fix_ave_spatial.html">fix ave/spatial</A>, and <A HREF = "variable.html">atom-style
variable</A> commands.
</P>
<P>The list of possible attributes is the same as that used by the <A HREF = "dump.html">dump
custom</A> command, which describes their meaning, with some
additional quantities that are only defined for certain <A HREF = "atom_style.html">atom
styles</A>. Basically, this augmented list gives an
input script access to any per-atom quantity stored by LAMMPS.
</P>
<P>The values are stored in a per-atom vector or array as discussed
below. Zeroes are stored for atoms not in the specified group or for
quantities that are not defined for a particular particle in the group
(e.g. <I>shapex</I> if the particle is not an ellipsoid).
</P>
<P>The additional quantities only accessible via this command, and not
directly via the <A HREF = "dump.html">dump custom</A> command, are as follows.
</P>
<P><I>Shapex</I>, <I>shapey</I>, and <I>shapez</I> are defined for ellipsoidal particles
and define the 3d shape of each particle.
</P>
<P><I>Quatw</I>, <I>quati</I>, <I>quatj</I>, and <I>quatk</I> are defined for ellipsoidal
particles and body particles and store the 4-vector quaternion
representing the orientation of each particle. See the <A HREF = "set.html">set</A>
command for an explanation of the quaternion vector.
</P>
<P><I>End1x</I>, <I>end1y</I>, <I>end1z</I>, <I>end2x</I>, <I>end2y</I>, <I>end2z</I>, are defined for
line segment particles and define the end points of each line segment.
</P>
<P><I>Corner1x</I>, <I>corner1y</I>, <I>corner1z</I>, <I>corner2x</I>, <I>corner2y</I>,
<I>corner2z</I>, <I>corner3x</I>, <I>corner3y</I>, <I>corner3z</I>, are defined for
triangular particles and define the corner points of each triangle.
</P>
<P><I>Nbonds</I> is available for all molecular atom styles and refers to the
number of explicit bonds assigned to an atom. Note that if the
<A HREF = "newton.html">newton bond</A> command is set to <I>on</I>, which is the
default, then every bond in the system is assigned to only one of the
two atoms in the bond. Thus a bond between atoms I,J may be tallied
for either atom I or atom J. If <A HREF = "newton.html">newton bond off</A> is set,
it will be tallied with both atom I and atom J.
</P>
<P>The <I>i_name</I> and <I>d_name</I> attributes refer to custom integer and
floating-point properties that have been added to each atom via the
<A HREF = "fix_property_atom.html">fix property/atom</A> command. When that command
is used specific names are given to each attribute which are what is
specified as the "name" portion of <I>i_name</I> or <I>d_name</I>.
</P>
<P><B>Output info:</B>
</P>
<P>This compute calculates a per-atom vector or per-atom array depending
on the number of input values. If a single input is specified, a
per-atom vector is produced. If two or more inputs are specified, a
per-atom array is produced where the number of columns = the number of
inputs. The vector or array can be accessed by any command that uses
per-atom values from a compute as input. See <A HREF = "Section_howto.html#howto_15">this
section</A> for an overview of LAMMPS output
options.
</P>
<P>The vector or array values will be in whatever <A HREF = "units.html">units</A> the
corresponding attribute is in, e.g. velocity units for vx, charge
units for q, etc.
</P>
<P><B>Restrictions:</B> none
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "dump.html">dump custom</A>, <A HREF = "compute_reduce.html">compute reduce</A>, <A HREF = "fix_ave_atom.html">fix
ave/atom</A>, <A HREF = "fix_ave_spatial.html">fix ave/spatial</A>,
<A HREF = "fix_property_atom.html">fix property/atom</A>
</P>
<P><B>Default:</B> none
</P>
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