.. 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