1.. index:: improper_style cvff
2.. index:: improper_style cvff/intel
3.. index:: improper_style cvff/omp
4
5improper_style cvff command
6===========================
7
8Accelerator Variants: *cvff/intel*, *cvff/omp*
9
10Syntax
11""""""
12
13.. code-block:: LAMMPS
14
15   improper_style cvff
16
17Examples
18""""""""
19
20.. code-block:: LAMMPS
21
22   improper_style cvff
23   improper_coeff 1 80.0 -1 4
24
25Description
26"""""""""""
27
28The *cvff* improper style uses the potential
29
30.. math::
31
32   E = K [1 + d  \cos (n \phi) ]
33
34where phi is the improper dihedral angle.
35
36If the 4 atoms in an improper quadruplet (listed in the data file read
37by the :doc:`read_data <read_data>` command) are ordered I,J,K,L then
38the improper dihedral angle is between the plane of I,J,K and the
39plane of J,K,L.  Note that because this is effectively a dihedral
40angle, the formula for this improper style is the same as for
41:doc:`dihedral_style harmonic <dihedral_harmonic>`.
42
43Note that defining 4 atoms to interact in this way, does not mean that
44bonds necessarily exist between I-J, J-K, or K-L, as they would in a
45linear dihedral.  Normally, the bonds I-J, I-K, I-L would exist for an
46improper to be defined between the 4 atoms.
47
48The following coefficients must be defined for each improper type via
49the :doc:`improper_coeff <improper_coeff>` command as in the example
50above, or in the data file or restart files read by the
51:doc:`read_data <read_data>` or :doc:`read_restart <read_restart>`
52commands:
53
54* :math:`K` (energy)
55* :math:`d` (+1 or -1)
56* :math:`n` (0,1,2,3,4,6)
57
58----------
59
60.. include:: accel_styles.rst
61
62----------
63
64Restrictions
65""""""""""""
66
67This improper style can only be used if LAMMPS was built with the
68MOLECULE package.  See the :doc:`Build package <Build_package>` doc page
69for more info.
70
71Related commands
72""""""""""""""""
73
74:doc:`improper_coeff <improper_coeff>`
75
76Default
77"""""""
78
79none
80