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