102 lines
3.0 KiB
ReStructuredText
102 lines
3.0 KiB
ReStructuredText
.. index:: bond_coeff
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bond_coeff command
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==================
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Syntax
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""""""
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.. code-block:: LAMMPS
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bond_coeff N args
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* N = numeric bond type (see asterisk form below), or type label
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* args = coefficients for one or more bond types
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Examples
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""""""""
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.. code-block:: LAMMPS
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bond_coeff 5 80.0 1.2
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bond_coeff * 30.0 1.5 1.0 1.0
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bond_coeff 1*4 30.0 1.5 1.0 1.0
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bond_coeff 1 harmonic 200.0 1.0 # (for bond_style hybrid)
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labelmap bond 5 carbonyl
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bond_coeff carbonyl 80.0 1.2
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Description
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"""""""""""
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Specify the bond force field coefficients for one or more bond types.
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The number and meaning of the coefficients depends on the bond style.
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Bond coefficients can also be set in the data file read by the
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:doc:`read_data <read_data>` command or in a restart file.
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:math:`N` can be specified in one of several ways. An explicit numeric
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value can be used, as in the first example above. Or :math:`N` can be a
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type label, which is an alphanumeric string defined by the
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:doc:`labelmap <labelmap>` command or in a section of a data file read
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by the :doc:`read_data <read_data>` command.
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For numeric values only, a wild-card asterisk can be used to set the
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coefficients for multiple bond types. This takes the form "\*" or "\*n"
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or "n\*" or "m\*n". If :math:`N` is the number of bond types, then an
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asterisk with no numeric values means all types from 1 to :math:`N`. A
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leading asterisk means all types from 1 to n (inclusive). A trailing
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asterisk means all types from n to :math:`N` (inclusive). A middle
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asterisk means all types from m to n (inclusive).
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Note that using a bond_coeff command can override a previous setting
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for the same bond type. For example, these commands set the coeffs
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for all bond types, then overwrite the coeffs for just bond type 2:
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.. code-block:: LAMMPS
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bond_coeff * 100.0 1.2
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bond_coeff 2 200.0 1.2
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A line in a data file that specifies bond coefficients uses the exact
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same format as the arguments of the bond_coeff command in an input
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script, except that wild-card asterisks should not be used since
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coefficients for all :math:`N` types must be listed in the file. For
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example, under the "Bond Coeffs" section of a data file, the line that
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corresponds to the first example above would be listed as
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.. parsed-literal::
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5 80.0 1.2
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----------
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The list of all bond styles defined in LAMMPS is given on the
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:doc:`bond_style <bond_style>` doc page. They are also listed in more
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compact form on the :doc:`Commands bond <Commands_bond>` doc page.
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On either of those pages, click on the style to display the formula it
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computes and its coefficients as specified by the associated
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bond_coeff command.
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----------
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Restrictions
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""""""""""""
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This command must come after the simulation box is defined by a
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:doc:`read_data <read_data>`, :doc:`read_restart <read_restart>`, or
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:doc:`create_box <create_box>` command.
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A bond style must be defined before any bond coefficients are set,
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either in the input script or in a data file.
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Related commands
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""""""""""""""""
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:doc:`bond_style <bond_style>`
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Default
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"""""""
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none
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