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"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.
For 3d aspherical particles, each has 3, 5, or 6 degrees of freedom (3
translational, remainder rotational), depending on whether the
particle is spherical, uniaxial, or biaxial. This is determined by
the "shape"_shape.html command. Uniaxial means two of its three shape
parameters are equal. Biaxial means all 3 shape parameters are
different.
For 2d aspherical particles, each has 3 or 4 degrees of freedom (3
translational, remainder rotational), depending on whether the
particle is spherical, or biaxial. Biaxial means the x,y shape
parameters are unequal.
IMPORTANT NOTE: These degrees of freedom assume that the interaction
potential between degenerate aspherical particles does not impart
rotational motion to the extra degrees of freedom. E.g. the "GayBerne
pair potential"_pair_gayberne.html does not impart torque to spherical
particles, so they do not rotate.
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 6-component kinetic energy tensor 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 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:]
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
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