107 lines
3.3 KiB
ReStructuredText
107 lines
3.3 KiB
ReStructuredText
.. index:: improper_coeff
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improper_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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improper_coeff N args
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* N = numeric improper type (see asterisk form below), or type label
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* args = coefficients for one or more improper types
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Examples
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""""""""
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.. code-block:: LAMMPS
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improper_coeff 1 300.0 0.0
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improper_coeff * 80.2 -1 2
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improper_coeff *4 80.2 -1 2
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labelmap improper 1 benzene
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improper_coeff benzene 300.0 0.0
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Description
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"""""""""""
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Specify the improper force field coefficients for one or more improper
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types. The number and meaning of the coefficients depends on the
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improper style. Improper coefficients can also be set in the data file
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read by the :doc:`read_data <read_data>` command or in a restart file.
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:math:`N` can be specified in one of two 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 improper types. This takes the form "\*" or
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"\*n" or "n\*" or "m\*n". If :math:`N` = the number of improper types,
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then an asterisk with no numeric values means all types from 1 to
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:math:`N`. A leading asterisk means all types from 1 to n (inclusive).
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A trailing asterisk means all types from n to :math:`N` (inclusive). A
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middle asterisk means all types from m to n (inclusive).
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Note that using an improper_coeff command can override a previous
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setting for the same improper type. For example, these commands set the
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coeffs for all improper types, then overwrite the coeffs for just
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improper type 2:
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.. code-block:: LAMMPS
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improper_coeff * 300.0 0.0
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improper_coeff 2 50.0 0.0
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A line in a data file that specifies improper coefficients uses the
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exact same format as the arguments of the improper_coeff command in an
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input 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 "Improper Coeffs" section of a data file, the line
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that corresponds to the first example above would be listed as
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.. parsed-literal::
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1 300.0 0.0
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The :doc:`improper_style class2 <improper_class2>` is an exception to
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this rule, in that an additional argument is used in the input script
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to allow specification of the cross-term coefficients. See its doc
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page for details.
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----------
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The list of all improper styles defined in LAMMPS is given on the
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:doc:`improper_style <improper_style>` doc page. They are also listed
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in more compact form on the :ref:`Commands improper <improper>` 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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improper_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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An improper style must be defined before any improper coefficients are
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set, 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:`improper_style <improper_style>`
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Default
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"""""""
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none
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