83 lines
1.9 KiB
ReStructuredText
83 lines
1.9 KiB
ReStructuredText
.. index:: angle_style spica
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.. index:: angle_style spica/omp
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angle_style spica command
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=========================
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Accelerator Variants: *spica/omp*
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Syntax
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""""""
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.. code-block:: LAMMPS
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angle_style spica
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angle_style spica/omp
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Examples
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""""""""
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.. code-block:: LAMMPS
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angle_style spica
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angle_coeff 1 300.0 107.0
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Description
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"""""""""""
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The *spica* angle style is a combination of the harmonic angle potential,
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.. math::
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E = K (\theta - \theta_0)^2
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where :math:`\theta_0` is the equilibrium value of the angle and
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:math:`K` a prefactor, with the *repulsive* part of the non-bonded
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*lj/spica* pair style between the atoms 1 and 3. This angle potential is
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intended for coarse grained MD simulations with the SPICA (formerly called SDK) parameterization
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using the :doc:`pair_style lj/spica <pair_spica>`. Relative to the
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pair_style *lj/spica*, however, the energy is shifted by
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:math:`\epsilon`, to avoid sudden jumps. Note that the usual 1/2 factor
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is included in :math:`K`.
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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:
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* :math:`K` (energy)
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* :math:`\theta_0` (degrees)
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:math:`\theta_0` is specified in degrees, but LAMMPS converts it to
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radians internally; hence :math:`K` is effectively energy per
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radian\^2.
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The required *lj/spica* parameters are extracted automatically from the
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pair_style.
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Style *sdk*, the original implementation of style *spica*, is available
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for backward compatibility.
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----------
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.. include:: accel_styles.rst
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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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CG-SPICA package. See the :doc:`Build package <Build_package>` doc
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page for more info.
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Related commands
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""""""""""""""""
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:doc:`angle_coeff <angle_coeff>`, :doc:`angle_style harmonic <angle_harmonic>`, :doc:`pair_style lj/spica <pair_spica>`,
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:doc:`pair_style lj/spica/coul/long <pair_spica>`
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Default
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"""""""
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none
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