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+.. index:: angle_style cosine/squared/restricted
+
+angle_style cosine/squared/restricted command
+==================================
+
+Syntax
+""""""
+
+.. code-block:: LAMMPS
+
+   angle_style cosine/squared/restricted
+
+Examples
+""""""""
+
+.. code-block:: LAMMPS
+
+   angle_style cosine/squared/restricted
+   angle_coeff 2*4 75.0 100.0
+
+Description
+"""""""""""
+
+The *cosine/squared/restricted* angle style uses the potential
+
+.. math::
+
+   E = K [\cos(\theta) - \cos(\theta_0)]^2 / \sin^2(\theta)
+
+, which is commonly used in the MARTINI force field,
+where :math:`\theta_0` is the equilibrium value of the angle, and :math:`K`
+is a prefactor.  Note that the usual 1/2 factor is included in :math:`K`.
+
+See :ref:`(Bulacu) <restricted-Bulacu>` for a description of the restricted angle for the MARTINI force field.
+
+The following coefficients must be defined for each angle type via the
+:doc:`angle_coeff <angle_coeff>` command as in the example above, or in
+the data file or restart files read by the :doc:`read_data <read_data>`
+or :doc:`read_restart <read_restart>` commands:
+
+* :math:`K` (energy)
+* :math:`\theta_0` (degrees)
+
+:math:`\theta_0` is specified in degrees, but LAMMPS converts it to radians
+internally.
+
+----------
+
+Restrictions
+""""""""""""
+
+This angle style can only be used if LAMMPS was built with the
+EXTRA-MOLECULE package.  See the :doc:`Build package <Build_package>` doc page
+for more info.
+
+Related commands
+""""""""""""""""
+
+:doc:`angle_coeff <angle_coeff>`
+
+Default
+"""""""
+
+none
+
+----------
+
+.. _restricted-Bulacu:
+
+**(Bulacu)** Bulacu, Goga, Zhao, Rossi, Monticelli, Periole, Tieleman, Marrink, J Chem Theory Comput, 9, 3282-3292
+(2013).