forked from lijiext/lammps
204 lines
5.1 KiB
Plaintext
204 lines
5.1 KiB
Plaintext
.. index:: pair_style lj/mdf
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pair_style lj/mdf command
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=========================
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pair_style buck/mdf command
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===========================
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pair_style lennard/mdf 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 = *lj/mdf* or *buck/mdf* or *lennard/mdf*
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* args = list of arguments for a particular style
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.. parsed-literal::
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*lj/mdf* args = cutoff1 cutoff2
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cutoff1 = inner cutoff for the start of the tapering function
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cutoff1 = out cutoff for the end of the tapering function
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*buck/mdf* args = cutoff1 cutoff2
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cutoff1 = inner cutoff for the start of the tapering function
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cutoff1 = out cutoff for the end of the tapering function
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*lennard/mdf* args = cutoff1 cutoff2
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cutoff1 = inner cutoff for the start of the tapering function
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cutoff1 = out cutoff for the end of the tapering function
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Examples
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""""""""
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.. parsed-literal::
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pair_style lj/mdf 2.5 3.0
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pair_coeff * * 1 1
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pair_coeff 1 1 1 1.1 2.8 3.0 3.2
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.. parsed-literal::
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pair_style buck 2.5 3.0
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pair_coeff * * 100.0 1.5 200.0
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pair_coeff * * 100.0 1.5 200.0 3.0 3.5
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.. parsed-literal::
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pair_style lennard/mdf 2.5 3.0
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pair_coeff * * 1 1
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pair_coeff 1 1 1 1.1 2.8 3.0 3.2
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Description
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"""""""""""
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The *lj/mdf*\ , *buck/mdf* and *lennard/mdf* compute the standard 12-6
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Lennard-Jones and Buckingham potential with the addition of a taper
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function that ramps the energy and force smoothly to zero between an
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inner and outer cutoff.
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.. image:: Eqs/pair_mdf-1.jpg
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:align: center
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The tapering, *f(r)*\ , is done by using the Mei, Davenport, Fernando
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function :ref:`(Mei) <Mei>`.
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.. image:: Eqs/pair_mdf-2.jpg
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:align: center
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where
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.. image:: Eqs/pair_mdf-3.jpg
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:align: center
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Here *r_m* is the inner cutoff radius and *r_cut* is the outer cutoff
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radius.
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----------
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For the *lj/mdf* pair_style, the potential energy, *E(r)*\ , is the
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standard 12-6 Lennard-Jones written in the epsilon/sigma form:
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.. image:: Eqs/pair_mdf-4.jpg
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:align: center
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The following coefficients must be defined for each pair of atoms
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types via the pair_coeff command as in the examples above, or in the
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data file or restart files read by the :doc:`read_data <read_data>` or
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:doc:`read_restart commands <read_restart>`, or by mixing as described
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below:
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* epsilon (energy units)
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* sigma (distance units)
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* r_m (distance units)
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* r_\ *cut* (distance units)
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----------
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For the *buck/mdf* pair_style, the potential energy, *E(r)*\ , is the
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standard Buckingham potential:
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.. image:: Eqs/pair_mdf-5.jpg
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:align: center
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* A (energy units)
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* \rho (distance units)
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* C (energy-distance^6 units)
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* r_m (distance units)
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* r_\ *cut*\ $ (distance units)
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----------
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For the *lennard/mdf* pair_style, the potential energy, *E(r)*\ , is the
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standard 12-6 Lennard-Jones written in the $A/B$ form:
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.. image:: Eqs/pair_mdf-6.jpg
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:align: center
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The following coefficients must be defined for each pair of atoms
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types via the pair_coeff command as in the examples above, or in the
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data file or restart files read by the read_data or read_restart
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commands, or by mixing as described below:
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* A (energy-distance^12 units)
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* B (energy-distance^6 units)
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* r_m (distance units)
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* r_\ *cut* (distance units)
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----------
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**Mixing, shift, table, tail correction, restart, rRESPA info**\ :
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For atom type pairs I,J and I != J, the epsilon and sigma coefficients
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and cutoff distance for all of the lj/cut pair styles can be mixed.
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The default mix value is *geometric*\ . See the "pair_modify" command
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for details.
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All of the *lj/cut* pair styles support the
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:doc:`pair_modify <pair_modify>` shift option for the energy of the
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Lennard-Jones portion of the pair interaction.
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The *lj/cut/coul/long* and *lj/cut/tip4p/long* pair styles support the
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:doc:`pair_modify <pair_modify>` table option since they can tabulate
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the short-range portion of the long-range Coulombic interaction.
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All of the *lj/cut* pair styles support the
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:doc:`pair_modify <pair_modify>` tail option for adding a long-range
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tail correction to the energy and pressure for the Lennard-Jones
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portion of the pair interaction.
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All of the *lj/cut* pair styles write their information to :doc:`binary restart files <restart>`, so pair_style and pair_coeff commands do
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not need to be specified in an input script that reads a restart file.
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The *lj/cut* and *lj/cut/coul/long* pair styles support the use of the
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*inner*\ , *middle*\ , and *outer* keywords of the :doc:`run_style respa <run_style>` command, meaning the pairwise forces can be
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partitioned by distance at different levels of the rRESPA hierarchy.
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The other styles only support the *pair* keyword of run_style respa.
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See the :doc:`run_style <run_style>` command for details.
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----------
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Restrictions
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""""""""""""
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These pair styles can only be used if LAMMPS was built with the
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USER-MISC package. See the :ref:`Making LAMMPS <start_3>`
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section for more info on packages.
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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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----------
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.. _Mei:
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**(Mei)** Mei, Davenport, Fernando, Phys Rev B, 43 4653 (1991)
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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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