.. index:: compute property/atom

compute property/atom command
=============================

Syntax
""""""

.. parsed-literal::

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

* ID, group-ID are documented in :doc:`compute <compute>` command
* property/atom = style name of this compute command
* input = one or more atom attributes

  .. parsed-literal::

       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,
                             sp, spx, spy, spz, fmx, fmy, fmz,
                             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,
                             buckling,
                             vfrac, s0,
                             spin, eradius, ervel, erforce,
                             rho, drho, e, de, cv,
                             i_name, d_name

  .. parsed-literal::

           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
           sp = atomic magnetic spin moment
           spx, spy, spz = direction of the atomic magnetic spin
           fmx, fmy, fmz = magnetic force
           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
           buckling = buckling flag used in mesoscopic simulation of nanotubes 

  .. parsed-literal::

           PERI package per-atom properties:
           vfrac = volume fraction
           s0 = max stretch of any bond a particle is part of

  .. parsed-literal::

           USER-EFF and USER-AWPMD package per-atom properties:
           spin = electron spin
           eradius = electron radius
           ervel = electron radial velocity
           erforce = electron radial force

  .. parsed-literal::

           USER-SPH package per-atom properties:
           rho = density of SPH particles
           drho = change in density
           e = energy
           de = change in thermal energy
           cv = heat capacity

  .. parsed-literal::

           :doc:`fix property/atom <fix_property_atom>` per-atom properties:
           i_name = custom integer vector with name
           d_name = custom integer vector with name

Examples
""""""""

.. code-block:: LAMMPS

   compute 1 all property/atom xs vx fx mux
   compute 2 all property/atom type
   compute 1 all property/atom ix iy iz
   compute 3 all property/atom sp spx spy spz

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
:doc:`output commands <Howto_output>` that take computes as inputs.
See for example, the :doc:`compute reduce <compute_reduce>`, :doc:`fix
ave/atom <fix_ave_atom>`, :doc:`fix ave/histo <fix_ave_histo>`,
:doc:`fix ave/chunk <fix_ave_chunk>`, and :doc:`atom-style variable
<variable>` commands.

The list of possible attributes is the same as that used by the
:doc:`dump custom <dump>` command, which describes their meaning, with
some additional quantities that are only defined for certain
:doc:`atom styles <atom_style>`.  Basically, this augmented list gives
an 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 or for
quantities that are not defined for a particular particle in the group
(e.g. *shapex* if the particle is not an ellipsoid).

The additional quantities only accessible via this command, and not
directly via the :doc:`dump custom <dump>` 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 defined for ellipsoidal
particles and body particles and store the 4-vector quaternion
representing the orientation of each particle.  See the :doc:`set <set>`
command for an explanation of the quaternion vector.

*End1x*\ , *end1y*\ , *end1z*\ , *end2x*\ , *end2y*\ , *end2z*\ , are
defined for line segment particles and define the end points of each
line segment.

*Corner1x*\ , *corner1y*\ , *corner1z*\ , *corner2x*\ , *corner2y*\ ,
*corner2z*\ , *corner3x*\ , *corner3y*\ , *corner3z*\ , are defined for
triangular particles and define the corner points of each triangle.

*Nbonds* is available for all molecular atom styles and refers to the
number of explicit bonds assigned to an atom.  Note that if the
:doc:`newton bond <newton>` command is set to *on*\ , 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 :doc:`newton bond off <newton>` is
set, it will be tallied with both atom I and atom J.

The *i_name* and *d_name* attributes refer to custom integer and
floating-point properties that have been added to each atom via the
:doc:`fix property/atom <fix_property_atom>` command.  When that
command is used specific names are given to each attribute which are
what is specified as the "name" portion of *i_name* or *d_name*.

**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 the :doc:`Howto output
<Howto_output>` doc page for an overview of LAMMPS output options.

The vector or array values will be in whatever :doc:`units <units>` the
corresponding attribute is in, e.g. velocity units for vx, charge
units for q, etc.

For the spin quantities, sp is in the units of the Bohr magneton, spx,
spy, and spz are unitless quantities, and fmx, fmy and fmz are given
in rad/THz.

Restrictions
""""""""""""
 none

Related commands
""""""""""""""""

:doc:`dump custom <dump>`, :doc:`compute reduce <compute_reduce>`,
:doc::doc:`fix ave/atom <fix_ave_atom>`, :doc:`fix ave/chunk
:doc:<fix_ave_chunk>`, `fix property/atom <fix_property_atom>`

**Default:** none
