93 lines
2.5 KiB
ReStructuredText
93 lines
2.5 KiB
ReStructuredText
.. index:: bond_style harmonic/shift
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bond_style harmonic/shift command
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=================================
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bond_style harmonic/shift/omp 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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bond_style harmonic/shift
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Examples
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""""""""
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.. code-block:: LAMMPS
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bond_style harmonic/shift
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bond_coeff 5 10.0 0.5 1.0
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Description
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"""""""""""
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The *harmonic/shift* bond style is a shifted harmonic bond that uses
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the potential
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.. math::
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E = \frac{U_{\text{min}}}{(r_0-r_c)^2} \left[ (r-r_0)^2-(r_c-r_0)^2 \right]
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where :math:`r_0` is the equilibrium bond distance, and :math:`r_c` the critical distance.
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The potential is :math:`-U_{\text{min}}` at :math:`r0` and zero at :math:`r_c`. The spring constant is
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:math:`k = U_{\text{min}} / [ 2 (r_0-r_c)^2]`.
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The following coefficients must be defined for each bond type via the
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:doc:`bond_coeff <bond_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:`U_{\text{min}}` (energy)
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* :math:`r_0` (distance)
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* :math:`r_c` (distance)
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----------
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Styles with a *gpu*\ , *intel*\ , *kk*\ , *omp*\ , or *opt* suffix are
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functionally the same as the corresponding style without the suffix.
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They have been optimized to run faster, depending on your available
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hardware, as discussed on the :doc:`Speed packages <Speed_packages>` doc
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page. The accelerated styles take the same arguments and should
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produce the same results, except for round-off and precision issues.
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These accelerated styles are part of the GPU, USER-INTEL, KOKKOS,
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USER-OMP and OPT packages, respectively. They are only enabled if
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LAMMPS was built with those packages. See the :doc:`Build package <Build_package>` doc page for more info.
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You can specify the accelerated styles explicitly in your input script
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by including their suffix, or you can use the :doc:`-suffix command-line switch <Run_options>` when you invoke LAMMPS, or you can use the
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:doc:`suffix <suffix>` command in your input script.
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See the :doc:`Speed packages <Speed_packages>` doc page for more
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instructions on how to use the accelerated styles effectively.
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----------
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Restrictions
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""""""""""""
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This bond style can only be used if LAMMPS was built with the
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USER-MISC 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:`bond_coeff <bond_coeff>`, :doc:`delete_bonds <delete_bonds>`,
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:doc:`bond_harmonic <bond_harmonic>`
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**Default:** none
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