.. index:: pair_style lj/class2 pair_style lj/class2 command ============================ pair_style lj/class2/gpu command ================================ pair_style lj/class2/kk command =============================== pair_style lj/class2/omp command ================================ pair_style lj/class2/coul/cut command ===================================== pair_style lj/class2/coul/cut/kk command ======================================== pair_style lj/class2/coul/cut/omp command ========================================= pair_style lj/class2/coul/long command ====================================== pair_style lj/class2/coul/long/gpu command ========================================== pair_style lj/class2/coul/long/kk command ========================================= pair_style lj/class2/coul/long/omp command ========================================== Syntax """""" .. parsed-literal:: pair_style style args * style = *lj/class2* or *lj/class2/coul/cut* or *lj/class2/coul/long* * args = list of arguments for a particular style .. parsed-literal:: *lj/class2* args = cutoff cutoff = global cutoff for class 2 interactions (distance units) *lj/class2/coul/cut* args = cutoff (cutoff2) cutoff = global cutoff for class 2 (and Coulombic if only 1 arg) (distance units) cutoff2 = global cutoff for Coulombic (optional) (distance units) *lj/class2/coul/long* args = cutoff (cutoff2) cutoff = global cutoff for class 2 (and Coulombic if only 1 arg) (distance units) cutoff2 = global cutoff for Coulombic (optional) (distance units) Examples """""""" .. parsed-literal:: pair_style lj/class2 10.0 pair_coeff * * 100.0 2.5 pair_coeff 1 2* 100.0 2.5 9.0 .. parsed-literal:: pair_style lj/class2/coul/cut 10.0 pair_style lj/class2/coul/cut 10.0 8.0 pair_coeff * * 100.0 3.0 pair_coeff 1 1 100.0 3.5 9.0 pair_coeff 1 1 100.0 3.5 9.0 9.0 .. parsed-literal:: pair_style lj/class2/coul/long 10.0 pair_style lj/class2/coul/long 10.0 8.0 pair_coeff * * 100.0 3.0 pair_coeff 1 1 100.0 3.5 9.0 Description """"""""""" The *lj/class2* styles compute a 6/9 Lennard-Jones potential given by .. image:: Eqs/pair_class2.jpg :align: center Rc is the cutoff. The *lj/class2/coul/cut* and *lj/class2/coul/long* styles add a Coulombic term as described for the :doc:`lj/cut ` pair styles. See :ref:`(Sun) ` for a description of the COMPASS class2 force field. The following coefficients must be defined for each pair of atoms types via the :doc:`pair_coeff ` command as in the examples above, or in the data file or restart files read by the :doc:`read_data ` or :doc:`read_restart ` commands, or by mixing as described below: * epsilon (energy units) * sigma (distance units) * cutoff1 (distance units) * cutoff2 (distance units) The latter 2 coefficients are optional. If not specified, the global class 2 and Coulombic cutoffs are used. If only one cutoff is specified, it is used as the cutoff for both class 2 and Coulombic interactions for this type pair. If both coefficients are specified, they are used as the class 2 and Coulombic cutoffs for this type pair. You cannot specify 2 cutoffs for style *lj/class2*\ , since it has no Coulombic terms. For *lj/class2/coul/long* only the class 2 cutoff can be specified since a Coulombic cutoff cannot be specified for an individual I,J type pair. All type pairs use the same global Coulombic cutoff specified in the pair_style command. ---------- If the pair_coeff command is not used to define coefficients for a particular I != J type pair, the mixing rule for epsilon and sigma for all class2 potentials is to use the *sixthpower* formulas documented by the :doc:`pair_modify ` command. The :doc:`pair_modify mix ` setting is thus ignored for class2 potentials for epsilon and sigma. However it is still followed for mixing the cutoff distance. ---------- Styles with a *gpu*\ , *intel*\ , *kk*\ , *omp*\ , or *opt* suffix are functionally the same as the corresponding style without the suffix. They have been optimized to run faster, depending on your available hardware, as discussed in :doc:`Section_accelerate ` of the manual. The accelerated styles take the same arguments and should produce the same results, except for round-off and precision issues. These accelerated styles are part of the GPU, USER-INTEL, KOKKOS, USER-OMP and OPT packages, respectively. They are only enabled if LAMMPS was built with those packages. See the :ref:`Making LAMMPS ` section for more info. You can specify the accelerated styles explicitly in your input script by including their suffix, or you can use the :ref:`-suffix command-line switch ` when you invoke LAMMPS, or you can use the :doc:`suffix ` command in your input script. See :doc:`Section_accelerate ` of the manual for more instructions on how to use the accelerated styles effectively. ---------- **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/class2 pair styles can be mixed. Epsilon and sigma are always mixed with the value *sixthpower*\ . The cutoff distance is mixed by whatever option is set by the pair_modify command (default = geometric). See the "pair_modify" command for details. All of the lj/class2 pair styles support the :doc:`pair_modify ` shift option for the energy of the Lennard-Jones portion of the pair interaction. The *lj/class2/coul/long* pair style does not support the :doc:`pair_modify ` table option since a tabulation capability has not yet been added to this potential. All of the lj/class2 pair styles support the :doc:`pair_modify ` tail option for adding a long-range tail correction to the energy and pressure of the Lennard-Jones portion of the pair interaction. All of the lj/class2 pair styles write their information to :doc:`binary restart files `, so pair_style and pair_coeff commands do not need to be specified in an input script that reads a restart file. All of the lj/class2 pair styles can only be used via the *pair* keyword of the :doc:`run_style respa ` command. They do not support the *inner*\ , *middle*\ , *outer* keywords. Restrictions """""""""""" These styles are part of the CLASS2 package. They are only enabled if LAMMPS was built with that package. See the :ref:`Making LAMMPS ` section for more info. Related commands """""""""""""""" :doc:`pair_coeff ` **Default:** none ---------- .. _pair-Sun: **(Sun)** Sun, J Phys Chem B 102, 7338-7364 (1998). .. _lws: http://lammps.sandia.gov .. _ld: Manual.html .. _lc: Section_commands.html#comm