"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

compute property/atom command :h3

[Syntax:]

compute ID group-ID property/atom input1 input2 ... :pre

ID, group-ID are documented in "compute"_compute.html command :ulb,l
property/atom = style name of this compute command :l
input = one or more atom attributes :l
  possible attributes = id, mol, 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,
			spin, eradius, ervel, erforce :pre

      id = atom ID
      mol = molecule ID
      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 extended particle
      angmomx,angmomy,angmomz = angular momentum of extended particle
      tqx,tqy,tqz = torque on extended particles
      spin = electron spin
      eradius = electron radius
      ervel = electron radial velocity
      erforce = electron radial force
      shapex,shapey,shapez = 3 diameters of aspherical particle
      quatw,quati,quatj,quatk = quaternion components for aspherical particles :pre
:ule

[Examples:]

compute 1 all property/atom xs vx fx mux 
compute 2 all property/atom type
compute 1 all property/atom ix iy iz :pre

[Description:]

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
"output commands"_Section_howto.html#4_15 that take computes as
inputs.  See for example, the "compute reduce"_compute_reduce.html,
"fix ave/atom"_fix_ave_atom.html, "fix ave/histo"_fix_ave_histo.html,
"fix ave/spatial"_fix_ave_spatial.html, and "atom-style
variable"_variable.html commands.

The list of possible attributes is the same as that used by the "dump
custom"_dump.html command, which describes their meaning, with some
additional quantities that are only defined for certain "atom
styles"_atom_style.html.  Basically, this list gives your input script
access to any per-atom quantity stored by LAMMPS.

The values are stored in a per-atom vector or array as
discussed below.  Zeroes are stored for atoms not in the specified
group.

The additional quantities only accessible via this command (and not
directly via the "dump custom"_dump.html command are as follows.

{Shapex}, {shapey}, and {shapez} are defined for ellipsoidal particles
and define the 3d shape of each particle.  {Quatw}, {quati}, {quatj},
and {quatk} are also defined for ellipsoidal particles and store the
4-vector quaternion representing the orientation of each particle.
See the "set"_set.html command for an explanation of the quaternion
vector.

[Output info:]

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 "this
section"_Section_howto.html#4_15 for an overview of LAMMPS output
options.

The vector or array values will be in whatever "units"_units.html the
corresponding attribute is in, e.g. velocity units for vx, charge
units for q, etc.

[Restrictions:] none

[Related commands:]

"dump custom"_dump.html, "compute reduce"_compute_reduce.html, "fix
ave/atom"_fix_ave_atom.html, "fix ave/spatial"_fix_ave_spatial.html

[Default:] none