Merge pull request #2435 from sramirezh/adding_new_pair

Adding new Wang-Frenkel potential pair style

doc/src/Commands_pair.rst

@@ -263,6 +263,7 @@ OPT.
    * :doc:`ufm (got) <pair_ufm>`
    * :doc:`vashishta (gko) <pair_vashishta>`
    * :doc:`vashishta/table (o) <pair_vashishta>`
+   * :doc:`wf/cut <pair_wf_cut>`
    * :doc:`yukawa (gko) <pair_yukawa>`
    * :doc:`yukawa/colloid (go) <pair_yukawa_colloid>`
    * :doc:`zbl (gko) <pair_zbl>`

doc/src/pair_style.rst

@@ -327,6 +327,7 @@ accelerated styles exist.
 * :doc:`ufm <pair_ufm>` -
 * :doc:`vashishta <pair_vashishta>` - Vashishta 2-body and 3-body potential
 * :doc:`vashishta/table <pair_vashishta>` -
+* :doc:`wf/cut <pair_wf_cut>` - Wang-Frenkel Potential for short-ranged interactions
 * :doc:`yukawa <pair_yukawa>` - Yukawa potential
 * :doc:`yukawa/colloid <pair_yukawa_colloid>` - screened Yukawa potential for finite-size particles
 * :doc:`zbl <pair_zbl>` - Ziegler-Biersack-Littmark potential

doc/src/pair_wf_cut.rst

@@ -0,0 +1,117 @@
+.. index:: pair_style wf/cut
+
+pair_style wf/cut command
+===========================
+
+Syntax
+""""""
+
+
+.. code-block:: LAMMPS
+
+   pair_style wf/cut cutoff
+
+* cutoff = cutoff for wf interactions (distance units)
+
+Examples
+""""""""
+
+
+.. code-block:: LAMMPS
+
+   pair_style        wf/cut 2.0
+   pair_coeff        1 1 1.0 1.0 1 1  2.0
+
+Description
+"""""""""""
+
+The *wf/cut* (Wang-Frenkel) style computes LJ-like potentials as
+described in :ref:`Wang2020 <Wang2020>`. This potential is by
+construction finite ranged and it vanishes quadratically at the cutoff
+distance, avoiding truncation, shifting, interpolation and other typical
+procedures with the LJ potential. The *wf/cut* can be used when a
+typical short-ranged potential with attraction is required. The
+potential is given by which is given by:
+
+.. math::
+  \phi(r)= \epsilon \alpha \left(\left[{\sigma\over r}\right]^{2\mu} -1 \right)\left(\left[{r_c\over r}\right]^{2\mu}-1\right)^{2\nu}
+
+with
+
+.. math::
+  \alpha=2\nu\left(\frac{r_c}{\sigma}\right)^{2\mu}\left[\frac{1+2\nu}{2\nu\left[(r_c/\sigma)^{2\mu}-1\right]}\right]^{2\nu+1}
+
+and
+
+.. math::
+  r_{min}=r_c\left[\frac{1+2\nu}{1+2\nu(r_c/\sigma)^{2\nu}}\right]^{1/{2\nu}}
+
+:math:`r_c` is the cutoff.
+
+Comparison of the non-truncated Lennard-Jones 12-6 potential (red curve),
+and the WF potentials with :math:`\mu=1` and :math:`\nu=1` are shown in
+the figure below. The blue curve has :math:`r_c =2.0` and the green
+curve has :math:`r_c =1.2` and can be used to describe colloidal
+interactions.
+
+.. image:: JPG/WF_LJ.jpg
+   :align: center
+   :scale: 33%
+
+
+The following coefficients must be defined for each pair of atoms
+types via the :doc:`pair_coeff <pair_coeff>` command as in the example
+above, or in the data file or restart files read by the
+:doc:`read_data <read_data>` or :doc:`read_restart <read_restart>`
+commands:
+
+* :math:`\epsilon` (energy units)
+* :math:`\sigma` (distance units)
+* :math:`\nu`
+* :math:`\mu`
+* :math:`r_c` (distance units)
+
+The last coefficient is optional. If not specified, the global cutoff
+given in the pair_style command is used.  The exponents :math:`\nu` and
+:math:`\mu` are positive integers, usually set to 1. There is usually
+little to be gained by choosing other values of :math:`\nu` and
+:math:`\mu` (See discussion in :ref:`Wang2020 <Wang2020>`)
+
+----------
+
+**Mixing, shift, table, tail correction, restart, rRESPA info**\ :
+
+This pair style does not support the :doc:`pair_modify <pair_modify>`
+mixing and table options.
+
+The :doc:`pair_modify <pair_modify>` tail option is not relevant
+for this pair style as it goes to zero at the cut-off radius.
+
+This pair style writes its 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.
+
+This pair style does not support the use of the *inner*\ , *middle*\ ,
+and *outer* keywords of the :doc:`run_style respa <run_style>` command.
+
+----------
+
+Restrictions
+""""""""""""
+This pair style can only be used if LAMMPS was built with the
+USER-MISC package.  See the :doc:`Build package <Build_package>` doc
+page for more info.
+
+Related commands
+""""""""""""""""
+
+:doc:`pair_coeff <pair_coeff>`
+
+**Default:** none
+
+
+----------
+
+.. _Wang2020:
+
+**(Wang2020)** X. Wang, S. Ramirez-Hinestrosa, J. Dobnikar, and D. Frenkel, Phys. Chem. Chem. Phys. 22, 10624 (2020).