lammps/doc/improper_coeff.txt

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:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)

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improper_coeff command :h3

[Syntax:]

improper_coeff N args :pre

N = improper type (see asterisk form below)
args = coefficients for one or more improper types :ul

[Examples:]

improper_coeff 1 300.0 0.0
improper_coeff * 80.2 -1 2
improper_coeff *4 80.2 -1 2 :pre

[Description:]

Specify the improper force field coefficients for one or more improper
types.  The number and meaning of the coefficients depends on the
improper style.  Improper coefficients can also be set in the data
file read by the "read_data"_read_data.html command or in a restart
file.

N can be specified in one of two ways.  An explicit numeric value can
be used, as in the 1st example above.  Or a wild-card asterisk can be
used to set the coefficients for multiple improper types.  This takes
the form "*" or "*n" or "n*" or "m*n".  If N = the number of improper
types, then an asterisk with no numeric values means all types from 1
to N.  A leading asterisk means all types from 1 to n (inclusive).  A
trailing asterisk means all types from n to N (inclusive).  A middle
asterisk means all types from m to n (inclusive).

Note that using an improper_coeff command can override a previous
setting for the same improper type.  For example, these commands set
the coeffs for all improper types, then overwrite the coeffs for just
improper type 2:

improper_coeff * 300.0 0.0
improper_coeff 2 50.0 0.0 :pre

A line in a data file that specifies improper coefficients uses the
exact same format as the arguments of the improper_coeff command in an
input script, except that wild-card asterisks should not be used since
coefficients for all N types must be listed in the file.  For example,
under the "Improper Coeffs" section of a data file, the line that
corresponds to the 1st example above would be listed as

1 300.0 0.0 :pre

The "improper_style class2"_improper_class2.html is an exception to
this rule, in that an additional argument is used in the input script
to allow specification of the cross-term coefficients.  See its doc
page for details.

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Here is an alphabetic list of improper styles defined in LAMMPS.  Click on
the style to display the formula it computes and coefficients
specified by the associated "improper_coeff"_improper_coeff.html command:

"improper_style none"_improper_none.html - turn off improper interactions
"improper_style hybrid"_improper_hybrid.html - define multiple styles of improper interactions :ul

"improper_style class2"_improper_class2.html - COMPASS (class 2) improper
"improper_style cvff"_improper_cvff.html - CVFF improper
"improper_style harmonic"_improper_harmonic.html - harmonic improper
"improper_style umbrella"_improper_umbrella.html - DREIDING improper :ul

There are also additional improper styles submitted by users which are
included in the LAMMPS distribution.  The list of these with links to
the individual styles are given in the improper section of "this
page"_Section_commands.html#cmd_5.

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[Restrictions:]

This command must come after the simulation box is defined by a
"read_data"_read_data.html, "read_restart"_read_restart.html, or
"create_box"_create_box.html command.

An improper style must be defined before any improper coefficients are
set, either in the input script or in a data file.

[Related commands:]

"improper_style"_improper_style.html

[Default:] none