forked from lijiext/lammps
123 lines
5.0 KiB
Plaintext
Executable File
123 lines
5.0 KiB
Plaintext
Executable File
"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 temp/asphere command :h3
|
|
|
|
[Syntax:]
|
|
|
|
compute ID group-ID temp/asphere bias-ID :pre
|
|
|
|
ID, group-ID are documented in "compute"_compute.html command
|
|
temp/asphere = style name of this compute command
|
|
bias-ID = ID of a temperature compute that removes a velocity bias (optional) :ul
|
|
|
|
[Examples:]
|
|
|
|
compute 1 all temp/asphere
|
|
compute myTemp mobile temp/asphere tempCOM :pre
|
|
|
|
[Description:]
|
|
|
|
Define a computation that calculates the temperature of a group of
|
|
aspherical particles, including a contribution from both their
|
|
translational and rotational kinetic energy. This differs from the
|
|
usual "compute temp"_compute_temp.html command, which assumes point
|
|
particles with only translational kinetic energy.
|
|
|
|
Only finite-size particles (aspherical or spherical) can be included
|
|
in the group. For 3d finite-size particles, each has 6 degrees of
|
|
freedom (3 translational, 3 rotational). For 2d finite-size
|
|
particles, each has 3 degrees of freedom (2 translational, 1
|
|
rotational).
|
|
|
|
IMPORTANT NOTE: This choice for degrees of freedom (dof) assumes that
|
|
all finite-size aspherical or spherical particles in your model will
|
|
freely rotate, sampling all their rotational dof. It is possible to
|
|
use a combination of interaction potentials and fixes that induce no
|
|
torque or otherwise constrain some of all of your particles so that
|
|
this is not the case. Then there are less dof and you should use the
|
|
"compute_modify extra"_compute_modify.html command to adjust the dof
|
|
accordingly.
|
|
|
|
For example, an aspherical particle with all three of its
|
|
"shape"_shape.html parameters the same is a sphere. If it does not
|
|
rotate, then it should have 3 dof instead of 6 in 3d (or 2 instead of
|
|
3 in 2d). A uniaxial aspherical particle has two of its three shape
|
|
parameters the same. If it does not rotate around the axis
|
|
perpendicular to its circular cross section, then it should have 5 dof
|
|
instead of 6 in 3d.
|
|
|
|
The translational kinetic energy is computed the same as is described
|
|
by the "compute temp"_compute_temp.html command. The rotational
|
|
kinetic energy is computed as 1/2 I w^2, where I is the inertia tensor
|
|
for the aspherical particle and w is its angular velocity, which is
|
|
computed from its angular momentum.
|
|
|
|
IMPORTANT NOTE: For "2d models"_dimension.html, particles are treated
|
|
as ellipsoids, not ellipses, meaning their moments of inertia will be
|
|
the same as in 3d.
|
|
|
|
A kinetic energy tensor, stored as a 6-element vector, is also
|
|
calculated by this compute. The formula for the components of the
|
|
tensor is the same as the above formula, except that v^2 and w^2 are
|
|
replaced by vx*vy and wx*wy for the xy component, and the appropriate
|
|
elements of the inertia tensor are used. The 6 components of the
|
|
vector are ordered xx, yy, zz, xy, xz, yz.
|
|
|
|
The number of atoms contributing to the temperature is assumed to be
|
|
constant for the duration of the run; use the {dynamic} option of the
|
|
"compute_modify"_compute_modify.html command if this is not the case.
|
|
|
|
If a {bias-ID} is specified it must be the ID of a temperature compute
|
|
that removes a "bias" velocity from each atom. This allows compute
|
|
temp/sphere to compute its thermal temperature after the translational
|
|
kinetic energy components have been altered in a prescribed way,
|
|
e.g. to remove a velocity profile. Thermostats that use this compute
|
|
will work with this bias term. See the doc pages for individual
|
|
computes that calculate a temperature and the doc pages for fixes that
|
|
perform thermostatting for more details.
|
|
|
|
This compute subtracts out translational degrees-of-freedom due to
|
|
fixes that constrain molecular motion, such as "fix
|
|
shake"_fix_shake.html and "fix rigid"_fix_rigid.html. This means the
|
|
temperature of groups of atoms that include these constraints will be
|
|
computed correctly. If needed, the subtracted degrees-of-freedom can
|
|
be altered using the {extra} option of the
|
|
"compute_modify"_compute_modify.html command.
|
|
|
|
See "this howto section"_Section_howto.html#4_16 of the manual for a
|
|
discussion of different ways to compute temperature and perform
|
|
thermostatting.
|
|
|
|
[Output info:]
|
|
|
|
This compute calculates a global scalar (the temperature) and a global
|
|
vector of length 6 (KE tensor), which can be accessed by indices 1-6.
|
|
These values can be used by any command that uses global scalar or
|
|
vector values from a compute as input. See "this
|
|
section"_Section_howto.html#4_15 for an overview of LAMMPS output
|
|
options.
|
|
|
|
The scalar value calculated by this compute is "intensive", meaning it
|
|
is independent of the number of atoms in the simulation. The vector
|
|
values are "extensive", meaning they scale with the number of atoms in
|
|
the simulation.
|
|
|
|
[Restrictions:]
|
|
|
|
This compute requires that particles be represented as extended
|
|
ellipsoids and not point particles. This means they will have an
|
|
angular momentum and a shape which is determined by the
|
|
"shape"_shape.html command.
|
|
|
|
[Related commands:]
|
|
|
|
"compute temp"_compute_temp.html
|
|
|
|
[Default:] none
|