118 lines
3.7 KiB
ReStructuredText
118 lines
3.7 KiB
ReStructuredText
.. index:: fix nve/sphere
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.. index:: fix nve/sphere/omp
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.. index:: fix nve/sphere/kk
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fix nve/sphere command
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======================
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Accelerator Variants: *nve/sphere/omp*, *nve/sphere/kk*
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Syntax
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""""""
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.. parsed-literal::
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fix ID group-ID nve/sphere
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* ID, group-ID are documented in :doc:`fix <fix>` command
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* nve/sphere = style name of this fix command
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* zero or more keyword/value pairs may be appended
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* keyword = *update* or *disc*
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.. parsed-literal::
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*update* value = *dipole* or *dipole/dlm*
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dipole = update orientation of dipole moment during integration
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dipole/dlm = use DLM integrator to update dipole orientation
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*disc* value = none = treat particles as 2d discs, not spheres
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Examples
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""""""""
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.. code-block:: LAMMPS
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fix 1 all nve/sphere
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fix 1 all nve/sphere update dipole
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fix 1 all nve/sphere disc
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fix 1 all nve/sphere update dipole/dlm
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Description
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"""""""""""
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Perform constant NVE integration to update position, velocity, and
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angular velocity for finite-size spherical particles in the group each
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timestep. V is volume; E is energy. This creates a system trajectory
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consistent with the microcanonical ensemble.
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This fix differs from the :doc:`fix nve <fix_nve>` command, which
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assumes point particles and only updates their position and velocity.
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If the *update* keyword is used with the *dipole* value, then the
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orientation of the dipole moment of each particle is also updated
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during the time integration. This option should be used for models
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where a dipole moment is assigned to finite-size particles,
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e.g. spheroids via use of the :doc:`atom_style hybrid sphere dipole
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<atom_style>` command.
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The default dipole orientation integrator can be changed to the
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Dullweber-Leimkuhler-McLachlan integration scheme
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:ref:`(Dullweber) <nh-Dullweber>` when using *update* with the value
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*dipole/dlm*\ . This integrator is symplectic and time-reversible,
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giving better energy conservation and allows slightly longer timesteps
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at only a small additional computational cost.
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If the *disc* keyword is used, then each particle is treated as a 2d
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disc (circle) instead of as a sphere. This is only possible for 2d
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simulations, as defined by the :doc:`dimension <dimension>` keyword.
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The only difference between discs and spheres in this context is their
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moment of inertia, as used in the time integration.
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----------
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.. include:: accel_styles.rst
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----------
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Restart, fix_modify, output, run start/stop, minimize info
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"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
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No information about this fix is written to :doc:`binary restart files
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<restart>`. None of the :doc:`fix_modify <fix_modify>` options are
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relevant to this fix. No global or per-atom quantities are stored by
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this fix for access by various :doc:`output commands <Howto_output>`.
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No parameter of this fix can be used with the *start/stop* keywords of
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the :doc:`run <run>` command. This fix is not invoked during
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:doc:`energy minimization <minimize>`.
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Restrictions
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""""""""""""
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This fix requires that atoms store torque and angular velocity (omega)
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and a radius as defined by the :doc:`atom_style sphere <atom_style>`
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command. If the *dipole* keyword is used, then they must also store a
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dipole moment as defined by the :doc:`atom_style dipole <atom_style>`
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command.
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All particles in the group must be finite-size spheres. They cannot
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be point particles.
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Use of the *disc* keyword is only allowed for 2d simulations, as
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defined by the :doc:`dimension <dimension>` keyword.
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Related commands
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""""""""""""""""
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:doc:`fix nve <fix_nve>`, :doc:`fix nve/asphere <fix_nve_asphere>`
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Default
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"""""""
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none
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----------
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.. _nve-Dullweber:
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**(Dullweber)** Dullweber, Leimkuhler and McLachlan, J Chem Phys, 107,
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5840 (1997).
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