1.. index:: improper_coeff
2
3improper_coeff command
4======================
5
6Syntax
7""""""
8
9.. code-block:: LAMMPS
10
11   improper_coeff N args
12
13* N = improper type (see asterisk form below)
14* args = coefficients for one or more improper types
15
16Examples
17""""""""
18
19.. code-block:: LAMMPS
20
21   improper_coeff 1 300.0 0.0
22   improper_coeff * 80.2 -1 2
23   improper_coeff *4 80.2 -1 2
24
25Description
26"""""""""""
27
28Specify the improper force field coefficients for one or more improper
29types.  The number and meaning of the coefficients depends on the
30improper style.  Improper coefficients can also be set in the data
31file read by the :doc:`read_data <read_data>` command or in a restart
32file.
33
34N can be specified in one of two ways.  An explicit numeric value can
35be used, as in the first example above.  Or a wild-card asterisk can be
36used to set the coefficients for multiple improper types.  This takes
37the form "\*" or "\*n" or "n\*" or "m\*n".  If N = the number of improper
38types, then an asterisk with no numeric values means all types from 1
39to N.  A leading asterisk means all types from 1 to n (inclusive).  A
40trailing asterisk means all types from n to N (inclusive).  A middle
41asterisk means all types from m to n (inclusive).
42
43Note that using an improper_coeff command can override a previous
44setting for the same improper type.  For example, these commands set
45the coeffs for all improper types, then overwrite the coeffs for just
46improper type 2:
47
48.. code-block:: LAMMPS
49
50   improper_coeff * 300.0 0.0
51   improper_coeff 2 50.0 0.0
52
53A line in a data file that specifies improper coefficients uses the
54exact same format as the arguments of the improper_coeff command in an
55input script, except that wild-card asterisks should not be used since
56coefficients for all N types must be listed in the file.  For example,
57under the "Improper Coeffs" section of a data file, the line that
58corresponds to the first example above would be listed as
59
60.. parsed-literal::
61
62   1 300.0 0.0
63
64The :doc:`improper_style class2 <improper_class2>` is an exception to
65this rule, in that an additional argument is used in the input script
66to allow specification of the cross-term coefficients.  See its doc
67page for details.
68
69----------
70
71The list of all improper styles defined in LAMMPS is given on the
72:doc:`improper_style <improper_style>` doc page.  They are also listed
73in more compact form on the :ref:`Commands improper <improper>` doc page.
74
75On either of those pages, click on the style to display the formula it
76computes and its coefficients as specified by the associated
77improper_coeff command.
78
79----------
80
81Restrictions
82""""""""""""
83
84This command must come after the simulation box is defined by a
85:doc:`read_data <read_data>`, :doc:`read_restart <read_restart>`, or
86:doc:`create_box <create_box>` command.
87
88An improper style must be defined before any improper coefficients are
89set, either in the input script or in a data file.
90
91Related commands
92""""""""""""""""
93
94:doc:`improper_style <improper_style>`
95
96Default
97"""""""
98
99none
100