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.. index:: pair_style lj/mdf
pair_style lj/mdf command
=========================
pair_style buck/mdf command
===========================
pair_style lennard/mdf command
==============================
Syntax
""""""
.. parsed-literal::
pair_style style args
* style = *lj/mdf* or *buck/mdf* or *lennard/mdf*
* args = list of arguments for a particular style
.. parsed-literal::
*lj/mdf* args = cutoff1 cutoff2
cutoff1 = inner cutoff for the start of the tapering function
cutoff1 = out cutoff for the end of the tapering function
*buck/mdf* args = cutoff1 cutoff2
cutoff1 = inner cutoff for the start of the tapering function
cutoff1 = out cutoff for the end of the tapering function
*lennard/mdf* args = cutoff1 cutoff2
cutoff1 = inner cutoff for the start of the tapering function
cutoff1 = out cutoff for the end of the tapering function
Examples
""""""""
.. parsed-literal::
pair_style lj/mdf 2.5 3.0
pair_coeff * * 1 1
pair_coeff 1 1 1 1.1 2.8 3.0 3.2
.. parsed-literal::
pair_style buck 2.5 3.0
pair_coeff * * 100.0 1.5 200.0
pair_coeff * * 100.0 1.5 200.0 3.0 3.5
.. parsed-literal::
pair_style lennard/mdf 2.5 3.0
pair_coeff * * 1 1
pair_coeff 1 1 1 1.1 2.8 3.0 3.2
Description
"""""""""""
The *lj/mdf*, *buck/mdf* and *lennard/mdf* compute the standard 12-6
Lennard-Jones and Buckingham potential with the addition of a taper
function that ramps the energy and force smoothly to zero between an
inner and outer cutoff.
.. image:: Eqs/pair_mdf-1.jpg
:align: center
The tapering, *f(r)*, is done by using the Mei, Davenport, Fernando
function :ref:`(Mei) <Mei>`.
.. image:: Eqs/pair_mdf-2.jpg
:align: center
where
.. image:: Eqs/pair_mdf-3.jpg
:align: center
Here *r_m* is the inner cutoff radius and *r_cut* is the outer cutoff
radius.
----------
For the *lj/mdf* pair_style, the potential energy, *E(r)*, is the
standard 12-6 Lennard-Jones written in the epsilon/sigma form:
.. image:: Eqs/pair_mdf-4.jpg
:align: center
The following coefficients must be defined for each pair of atoms
types via the pair_coeff command as in the examples above, or in the
data file or restart files read by the :doc:`read_data <read_data>` or
:doc:`read_restart commands <read_restart>`, or by mixing as described
below:
* epsilon (energy units)
* sigma (distance units)
* r_m (distance units)
* r_*cut* (distance units)
----------
For the *buck/mdf* pair_style, the potential energy, *E(r)*, is the
standard 12-6 Lennard-Jones written in the epsilon/sigma form:
.. image:: Eqs/pair_mdf-5.jpg
:align: center
* A (energy units)
* \rho (distance units)
* C (energy-distance^6 units)
* r_m (distance units)
* r_*cut*$ (distance units)
----------
For the *lennard/mdf* pair_style, the potential energy, *E(r)*, is the
standard 12-6 Lennard-Jones written in the $A/B$ form:
.. image:: Eqs/pair_mdf-6.jpg
:align: center
The following coefficients must be defined for each pair of atoms
types via the pair_coeff command as in the examples above, or in the
data file or restart files read by the read_data or read_restart
commands, or by mixing as described below:
* A (energy-distance^12 units)
* B (energy-distance^6 units)
* r_m (distance units)
* r_*cut* (distance units)
----------
**Mixing, shift, table, tail correction, restart, rRESPA info**:
For atom type pairs I,J and I != J, the epsilon and sigma coefficients
and cutoff distance for all of the lj/cut pair styles can be mixed.
The default mix value is *geometric*. See the "pair_modify" command
for details.
All of the *lj/cut* pair styles support the
:doc:`pair_modify <pair_modify>` shift option for the energy of the
Lennard-Jones portion of the pair interaction.
The *lj/cut/coul/long* and *lj/cut/tip4p/long* pair styles support the
:doc:`pair_modify <pair_modify>` table option since they can tabulate
the short-range portion of the long-range Coulombic interaction.
All of the *lj/cut* pair styles support the
:doc:`pair_modify <pair_modify>` tail option for adding a long-range
tail correction to the energy and pressure for the Lennard-Jones
portion of the pair interaction.
All of the *lj/cut* pair styles write their information to :doc:`binary restart files <restart>`, so pair_style and pair_coeff commands do
not need to be specified in an input script that reads a restart file.
The *lj/cut* and *lj/cut/coul/long* pair styles support the use of the
*inner*, *middle*, and *outer* keywords of the :doc:`run_style respa <run_style>` command, meaning the pairwise forces can be
partitioned by distance at different levels of the rRESPA hierarchy.
The other styles only support the *pair* keyword of run_style respa.
See the :doc:`run_style <run_style>` command for details.
----------
Restrictions
""""""""""""
These pair styles can only be used if LAMMPS was built with the
USER-MISC package. See the :ref:`Making LAMMPS <start_3>`
section for more info on packages.
Related commands
""""""""""""""""
:doc:`pair_coeff <pair_coeff>`
**Default:** none
----------
.. _Mei:
**(Mei)** Mei, Davenport, Fernando, Phys Rev B, 43 4653 (1991)
.. _lws: http://lammps.sandia.gov
.. _ld: Manual.html
.. _lc: Section_commands.html#comm
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