1.. index:: angle_style cosine/shift
2.. index:: angle_style cosine/shift/omp
3
4angle_style cosine/shift command
5================================
6
7Accelerator Variants: *cosine/shift/omp*
8
9Syntax
10""""""
11
12.. code-block:: LAMMPS
13
14   angle_style cosine/shift
15
16Examples
17""""""""
18
19.. code-block:: LAMMPS
20
21   angle_style cosine/shift
22   angle_coeff * 10.0 45.0
23
24Description
25"""""""""""
26
27The *cosine/shift* angle style uses the potential
28
29.. math::
30
31   E = -\frac{U_{\text{min}}}{2} \left[ 1 + \cos(\theta-\theta_0) \right]
32
33where :math:`\theta_0` is the equilibrium angle. The potential is bounded
34between :math:`-U_{\text{min}}` and zero. In the neighborhood of the minimum
35:math:`E = - U_{\text{min}} + U_{\text{min}}/4(\theta - \theta_0)^2` hence
36the spring constant is :math:`\frac{U_{\text{min}}}{2}`.
37
38The following coefficients must be defined for each angle type via the
39:doc:`angle_coeff <angle_coeff>` command as in the example above, or in
40the data file or restart files read by the :doc:`read_data <read_data>`
41or :doc:`read_restart <read_restart>` commands:
42
43* :math:`U_{\text{min}}` (energy)
44* :math:`\theta` (angle)
45
46----------
47
48.. include:: accel_styles.rst
49
50----------
51
52Restrictions
53""""""""""""
54
55This angle style can only be used if LAMMPS was built with the
56EXTRA-MOLECULE package.  See the :doc:`Build package <Build_package>` doc
57page for more info.
58
59Related commands
60""""""""""""""""
61
62:doc:`angle_coeff <angle_coeff>`,
63:doc:`angle_style cosine/shift/exp <angle_cosine_shift_exp>`
64
65Default
66"""""""
67
68none
69