forked from lijiext/lammps
67 lines
2.1 KiB
Plaintext
67 lines
2.1 KiB
Plaintext
"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 com command :h3
|
|
|
|
[Syntax:]
|
|
|
|
compute ID group-ID com :pre
|
|
|
|
ID, group-ID are documented in "compute"_compute.html command
|
|
com = style name of this compute command :ul
|
|
|
|
[Examples:]
|
|
|
|
compute 1 all com :pre
|
|
|
|
[Description:]
|
|
|
|
Define a computation that calculates the center-of-mass of the group
|
|
of atoms, including all effects due to atoms passing thru periodic
|
|
boundaries.
|
|
|
|
A vector of three quantites is calculated by this compute, which
|
|
are the x,y,z coordinates of the center of mass.
|
|
|
|
IMPORTANT NOTE: The coordinates of an atom contribute to the
|
|
center-of-mass in "unwrapped" form, by using the image flags
|
|
associated with each atom. See the "dump custom"_dump.html command
|
|
for a discussion of "unwrapped" coordinates. See the Atoms section of
|
|
the "read_data"_read_data.html command for a discussion of image flags
|
|
and how they are set for each atom. You can reset the image flags
|
|
(e.g. to 0) before invoking this compute by using the "set
|
|
image"_set.html command.
|
|
|
|
IMPORTANT NOTE: If an atom is part of a rigid body (see the "fix
|
|
rigid"_fix_rigid.html command), it's periodic image flags are altered,
|
|
and its contribution to the center-of-mass may not reflect its true
|
|
contribution. See the "fix rigid"_fix_rigid.html command for details.
|
|
Thus, to compute the center-of-mass of rigid bodies as they cross
|
|
periodic boundaries, you will need to post-process a "dump
|
|
file"_dump.html containing coordinates of the atoms in the bodies.
|
|
|
|
[Output info:]
|
|
|
|
This compute calculates a global vector of length 3, which can be
|
|
accessed by indices 1-3 by any command that uses global vector values
|
|
from a compute as input. See "this section"_Section_howto.html#4_15
|
|
for an overview of LAMMPS output options.
|
|
|
|
The vector values are "intensive", meaning they are independent of the
|
|
number of atoms in the simulation.
|
|
|
|
The vector values will be in distance "units"_units.html.
|
|
|
|
[Restrictions:] none
|
|
|
|
[Related commands:]
|
|
|
|
"compute com/molecule"_compute_com_molecule.html
|
|
|
|
[Default:] none
|