46 lines
1.8 KiB
ReStructuredText
46 lines
1.8 KiB
ReStructuredText
2d simulations
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==============
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Use the :doc:`dimension <dimension>` command to specify a 2d simulation.
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Make the simulation box periodic in z via the :doc:`boundary <boundary>`
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command. This is the default.
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If using the :doc:`create box <create_box>` command to define a
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simulation box, set the z dimensions narrow, but finite, so that the
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create\_atoms command will tile the 3d simulation box with a single z
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plane of atoms - e.g.
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.. parsed-literal::
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:doc:`create box <create_box>` 1 -10 10 -10 10 -0.25 0.25
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If using the :doc:`read data <read_data>` command to read in a file of
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atom coordinates, set the "zlo zhi" values to be finite but narrow,
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similar to the create\_box command settings just described. For each
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atom in the file, assign a z coordinate so it falls inside the
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z-boundaries of the box - e.g. 0.0.
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Use the :doc:`fix enforce2d <fix_enforce2d>` command as the last
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defined fix to insure that the z-components of velocities and forces
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are zeroed out every timestep. The reason to make it the last fix is
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so that any forces induced by other fixes will be zeroed out.
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Many of the example input scripts included in the LAMMPS distribution
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are for 2d models.
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.. note::
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Some models in LAMMPS treat particles as finite-size spheres, as
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opposed to point particles. See the :doc:`atom_style sphere <atom_style>` and :doc:`fix nve/sphere <fix_nve_sphere>`
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commands for details. By default, for 2d simulations, such particles
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will still be modeled as 3d spheres, not 2d discs (circles), meaning
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their moment of inertia will be that of a sphere. If you wish to
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model them as 2d discs, see the :doc:`set density/disc <set>` command
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and the *disc* option for the :doc:`fix nve/sphere <fix_nve_sphere>`,
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:doc:`fix nvt/sphere <fix_nvt_sphere>`, :doc:`fix nph/sphere <fix_nph_sphere>`, :doc:`fix npt/sphere <fix_npt_sphere>`
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commands.
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