95 lines
2.1 KiB
ReStructuredText
95 lines
2.1 KiB
ReStructuredText
.. index:: angle_style mwlc
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angle_style mwlc command
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==========================
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Syntax
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""""""
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.. code-block:: LAMMPS
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angle_style mwlc
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Examples
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""""""""
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.. code-block:: LAMMPS
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angle_style mwlc
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angle_coeff * 25 1 10 1
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Description
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"""""""""""
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.. versionadded:: 4Feb2025
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The *mwlc* angle style models a meltable wormlike chain and can be used
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to model non-linear bending elasticity of polymers, e.g. DNA. *mwlc*
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uses a potential that is a canonical-ensemble superposition of a
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non-melted and a melted state :ref:`(Farrell) <Farrell>`. The potential
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is
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.. math::
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E = -k_{B}T\,\log [q + q^{m}] + E_{0},
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where the non-melted and melted partition functions are
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.. math::
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q = \exp [-k_{1}(1+\cos{\theta})/k_{B}T]; \\
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q^{m} = \exp [-(\mu+k_{2}(1+\cos{\theta}))/k_{B}T].
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:math:`k_1` is the bending elastic constant of the non-melted state,
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:math:`k_2` is the bending elastic constant of the melted state,
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:math:`\mu` is the melting energy, and
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:math:`T` is the reference temperature.
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The reference energy,
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.. math::
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E_{0} = -k_{B}T\,\log [1 + \exp[-\mu/k_{B}T]],
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ensures that E is zero for a fully extended chain.
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This potential is a continuous version of the two-state potential
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introduced by :ref:`(Yan) <Yan>`.
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The following coefficients must be defined for each angle type via the
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:doc:`angle_coeff <angle_coeff>` command as in the example above, or in
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the data file or restart files read by the :doc:`read_data <read_data>`
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or :doc:`read_restart <read_restart>` commands:
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* :math:`k_1` (energy)
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* :math:`k_2` (energy)
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* :math:`\mu` (energy)
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* :math:`T` (temperature)
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----------
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Restrictions
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""""""""""""
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This angle style can only be used if LAMMPS was built with the
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EXTRA-MOLECULE package. See the :doc:`Build package <Build_package>`
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doc page for more info.
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Related commands
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""""""""""""""""
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:doc:`angle_coeff <angle_coeff>`
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Default
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"""""""
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none
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----------
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.. _Farrell:
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**(Farrell)** `Farrell, Dobnikar, Podgornik, Curk, Phys Rev Lett, 133, 148101 (2024). <https://doi.org/10.1103/PhysRevLett.133.148101>`_
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.. _Yan:
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**(Yan)** `Yan, Marko, Phys Rev Lett, 93, 108108 (2004). <https://doi.org/10.1103/PhysRevLett.93.108108>`_
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