forked from lijiext/lammps
195 lines
5.5 KiB
Plaintext
195 lines
5.5 KiB
Plaintext
.. index:: pair_style morse
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pair_style morse command
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========================
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pair_style morse/gpu command
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============================
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pair_style morse/omp command
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============================
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pair_style morse/opt command
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============================
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pair_style morse/smooth/linear command
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======================================
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pair_style morse/smooth/linear/omp command
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==========================================
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pair_style morse/soft command
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=============================
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Syntax
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""""""
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.. parsed-literal::
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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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*morse/soft* args = n lf cutoff
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n = soft-core parameter
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lf = transformation range is lf < lambda < 1
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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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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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.. parsed-literal::
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pair_style morse/soft 4 0.9 10.0
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pair_coeff * * 100.0 2.0 1.5 1.0
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pair_coeff 1 1 100.0 2.0 1.5 1.0 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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.. image:: Eqs/pair_morse.jpg
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:align: center
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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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* D0 (energy units)
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* alpha (1/distance units)
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* r0 (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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.. image:: Eqs/pair_morse_smooth_linear.jpg
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:align: center
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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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The *morse/soft* variant is similar to the *lj/cut/soft* pair style
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in that it modifies the potential at short range to have a soft core.
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This helps to avoid singularities during free energy calculation in
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which sites are created or anihilated. The formula differs from that
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of *lj/cut/soft*\ , and is instead given by:
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.. image:: Eqs/pair_morse_soft.jpg
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:align: center
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The *morse/soft* style requires the following pair coefficients:
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* D0 (energy units)
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* alpha (1/distance units)
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* r0 (distance units)
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* lamda (unitless, between 0.0 and 1.0)
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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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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 in :doc:`Section_accelerate <Section_accelerate>`
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of the manual. The accelerated styles take the same arguments and
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should produce the same results, except for round-off and precision
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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 :ref:`Making LAMMPS <start_3>` section 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 :ref:`-suffix command-line switch <start_7>` when you invoke LAMMPS, or you can
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use the :doc:`suffix <suffix>` command in your input script.
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See :doc:`Section_accelerate <Section_accelerate>` of the manual for
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more instructions on how to use the accelerated styles effectively.
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----------
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**Mixing, shift, table, tail correction, restart, rRESPA info**\ :
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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 :ref:`Making LAMMPS <start_3>` section for more info.
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The *morse/soft* pair style is only enabled if LAMMPS was built with
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the USER-FEP package. See the :ref:`Making LAMMPS <start_3>` section for more info.
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Related commands
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""""""""""""""""
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:doc:`pair_coeff <pair_coeff>`
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**Default:** none
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.. _lws: http://lammps.sandia.gov
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.. _ld: Manual.html
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.. _lc: Section_commands.html#comm
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