141 lines
4.0 KiB
ReStructuredText
141 lines
4.0 KiB
ReStructuredText
.. index:: pair_style morse
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.. index:: pair_style morse/gpu
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.. index:: pair_style morse/omp
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.. index:: pair_style morse/opt
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.. index:: pair_style morse/smooth/linear
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.. index:: pair_style morse/smooth/linear/omp
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.. index:: pair_style morse/kk
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pair_style morse command
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========================
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Accelerator Variants: *morse/gpu*, *morse/omp*, *morse/opt*, *morse/kk*
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pair_style morse/smooth/linear command
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======================================
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Accelerator Variants: *morse/smooth/linear/omp*
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Syntax
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""""""
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.. code-block:: LAMMPS
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pair_style style args
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* style = *morse* or *morse/smooth/linear* or *morse/soft*
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* args = list of arguments for a particular style
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.. parsed-literal::
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*morse* args = cutoff
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cutoff = global cutoff for Morse interactions (distance units)
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*morse/smooth/linear* args = cutoff
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cutoff = global cutoff for Morse interactions (distance units)
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Examples
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""""""""
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.. code-block:: LAMMPS
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pair_style morse 2.5
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pair_style morse/smooth/linear 2.5
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pair_coeff * * 100.0 2.0 1.5
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pair_coeff 1 1 100.0 2.0 1.5 3.0
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Description
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"""""""""""
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Style *morse* computes pairwise interactions with the formula
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.. math::
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E = D_0 \left[ e^{- 2 \alpha (r - r_0)} - 2 e^{- \alpha (r - r_0)} \right]
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\qquad r < r_c
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Rc is the cutoff.
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The following coefficients must be defined for each pair of atoms
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types via the :doc:`pair_coeff <pair_coeff>` command as in the examples
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above, or in the data file or restart files read by the
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:doc:`read_data <read_data>` or :doc:`read_restart <read_restart>`
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commands:
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* :math:`D_0` (energy units)
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* :math:`\alpha` (1/distance units)
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* :math:`r_0` (distance units)
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* cutoff (distance units)
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The last coefficient is optional. If not specified, the global morse
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cutoff is used.
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----------
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The *morse/smooth/linear* variant is similar to the lj/smooth/linear
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variant in that it adds to the potential a shift and a linear term
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so that both, potential energy and force, go to zero at the cut-off:
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.. math::
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\phi\left(r\right) & = D_0 \left[ e^{- 2 \alpha (r - r_0)} - 2 e^{- \alpha (r - r_0)} \right] \qquad r < r_c \\
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E\left(r\right) & = \phi\left(r\right) - \phi\left(R_c\right) - \left(r - R_c\right) \left.\frac{d\phi}{d r} \right|_{r=R_c} \qquad r < R_c
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The syntax of the pair_style and pair_coeff commands are the same for
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the *morse* and *morse/smooth/linear* styles.
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----------
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A version of the *morse* style with a soft core, *morse/soft*\ ,
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suitable for use in free energy calculations, is part of the USER-FEP
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package and is documented with the :doc:`pair_style */soft
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<pair_fep_soft>` styles. The version with soft core is only available if
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LAMMPS was built with that package. See the :doc:`Build package
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<Build_package>` doc page for more info.
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----------
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.. include:: accel_styles.rst
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----------
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Mixing, shift, table, tail correction, restart, rRESPA info
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"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
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None of these pair styles support mixing. Thus, coefficients for all
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I,J pairs must be specified explicitly.
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All of these pair styles support the :doc:`pair_modify <pair_modify>`
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shift option for the energy of the pair interaction.
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The :doc:`pair_modify <pair_modify>` table options is not relevant for
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the Morse pair styles.
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None of these pair styles support the :doc:`pair_modify <pair_modify>`
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tail option for adding long-range tail corrections to energy and
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pressure.
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All of these pair styles write their information to :doc:`binary restart files <restart>`, so pair_style and pair_coeff commands do not need
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to be specified in an input script that reads a restart file.
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These pair styles can only be used via the *pair* keyword of the
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:doc:`run_style respa <run_style>` command. They do not support the
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*inner*\ , *middle*\ , *outer* keywords.
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----------
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Restrictions
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""""""""""""
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The *morse/smooth/linear* pair style is only enabled if LAMMPS was
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built with the USER-MISC package. See the :doc:`Build package <Build_package>` doc page for more info.
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Related commands
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""""""""""""""""
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:doc:`pair_coeff <pair_coeff>`, :doc:`pair_style */soft <pair_fep_soft>`
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Default
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"""""""
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none
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