forked from lijiext/lammps
116 lines
3.6 KiB
Plaintext
116 lines
3.6 KiB
Plaintext
.. 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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.. parsed-literal::
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improper_coeff N args
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* N = improper type (see asterisk form below)
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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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.. parsed-literal::
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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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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
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file read by the :doc:`read_data <read_data>` command or in a restart
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file.
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N can be specified in one of two ways. An explicit numeric value can
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be used, as in the 1st example above. Or a wild-card asterisk can be
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used to set the coefficients for multiple improper types. This takes
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the form "*" or "*n" or "n*" or "m*n". If N = the number of improper
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types, then an asterisk with no numeric values means all types from 1
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to N. A leading asterisk means all types from 1 to n (inclusive). A
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trailing asterisk means all types from n to N (inclusive). A middle
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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
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the coeffs for all improper types, then overwrite the coeffs for just
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improper type 2:
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.. parsed-literal::
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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 N types must be listed in the file. For example,
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under the "Improper Coeffs" section of a data file, the line that
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corresponds to the 1st 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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Here is an alphabetic list of improper styles defined in LAMMPS. Click on
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the style to display the formula it computes and coefficients
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specified by the associated :doc:`improper_coeff <improper_coeff>` command.
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Note that there are also additional improper styles submitted by users
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which are included in the LAMMPS distribution. The list of these with
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links to the individual styles are given in the improper section of
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:ref:`this page <cmd_5>`.
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* :doc:`improper_style none <improper_none>` - turn off improper interactions
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* :doc:`improper_style hybrid <improper_hybrid>` - define multiple styles of improper interactions
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* :doc:`improper_style class2 <improper_class2>` - COMPASS (class 2) improper
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* :doc:`improper_style cvff <improper_cvff>` - CVFF improper
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* :doc:`improper_style harmonic <improper_harmonic>` - harmonic improper
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* :doc:`improper_style umbrella <improper_umbrella>` - DREIDING improper
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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:** none
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.. _lws: http://lammps.sandia.gov
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.. _ld: Manual.html
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.. _lc: Section_commands.html#comm
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