Add new pair styles harmonic/cut for repulsive-only harmonic interaction

doc/src/Commands_pair.rst

@@ -119,6 +119,7 @@ OPT.
    * :doc:`granular <pair_granular>`
    * :doc:`gw <pair_gw>`
    * :doc:`gw/zbl <pair_gw>`
+   * :doc:`harmonic/cut (o) <pair_harmonic_cut>`
    * :doc:`hbond/dreiding/lj (o) <pair_hbond_dreiding>`
    * :doc:`hbond/dreiding/morse (o) <pair_hbond_dreiding>`
    * :doc:`hdnnp <pair_hdnnp>`

doc/src/pair_harmonic_cut.rst

@@ -0,0 +1,90 @@
+.. index:: pair_style harmonic/cut
+.. index:: pair_style harmonic/cut/omp
+
+pair_style harmonic/cut command
+===============================
+
+Accelerator Variants: *harmonic/cut/omp*
+
+Syntax
+""""""
+
+.. code-block:: LAMMPS
+
+   pair_style style
+
+* style = *harmonic/cut*
+
+Examples
+""""""""
+
+.. code-block:: LAMMPS
+
+   pair_style harmonic/cut 2.5
+   pair_coeff * * 0.2 2.0
+   pair_coeff 1 1 0.5 2.5
+
+Description
+"""""""""""
+
+Style *harmonic/cut* computes pairwise repulsive-only harmonic interactions with the formula
+
+.. math::
+
+   E = k (r_c - r)^2  \qquad r < r_c
+
+:math:`r_c` is the cutoff.
+
+The following coefficients must be defined for each pair of atoms
+types via the :doc:`pair_coeff <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 <read_restart>`
+commands:
+
+* :math:`k` (energy units)
+* :math:`r_c` (distance units)
+
+----------
+
+.. include:: accel_styles.rst
+
+----------
+
+Mixing, shift, table, tail correction, restart, rRESPA info
+"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
+
+For atom type pairs I,J and I != J, the :math:`k` and :math:`r_c`
+coefficients can be mixed. The default mix value is *geometric*.
+See the "pair_modify" command for details.
+
+Since the potential is zero at and beyond the cutoff parameter by
+construction, there is no need to support support the :doc:`pair_modify
+<pair_modify>` shift or tail options for the energy and pressure of the
+pair interaction.
+
+These 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.
+
+These pair styles can only be used via the *pair* keyword of the
+:doc:`run_style respa <run_style>` command.  They do not support the
+*inner*, *middle*, *outer* keywords.
+
+----------
+
+Restrictions
+""""""""""""
+
+The *harmonic/cut* pair style is only enabled if LAMMPS was
+built with the EXTRA-PAIR package.
+See the :doc:`Build package <Build_package>` page for more info.
+
+Related commands
+""""""""""""""""
+
+:doc:`pair_coeff <pair_coeff>`
+
+Default
+"""""""
+
+none

doc/src/pair_style.rst

@@ -183,6 +183,7 @@ accelerated styles exist.
 * :doc:`gran/hooke/history <pair_gran>` - granular potential without history effects
 * :doc:`gw <pair_gw>` - Gao-Weber potential
 * :doc:`gw/zbl <pair_gw>` - Gao-Weber potential with a repulsive ZBL core
+* :doc:`harmonic/cut <pair_harmonic_cut>` - repulsive-only harmonic potential
 * :doc:`hbond/dreiding/lj <pair_hbond_dreiding>` - DREIDING hydrogen bonding LJ potential
 * :doc:`hbond/dreiding/morse <pair_hbond_dreiding>` - DREIDING hydrogen bonding Morse potential
 * :doc:`hdnnp <pair_hdnnp>` - High-dimensional neural network potential

src/.gitignore

@@ -1489,6 +1489,8 @@
 /pair_dpd_fdt.h
 /pair_dpd_fdt_energy.cpp
 /pair_dpd_fdt_energy.h
+/pair_harmonic_cut.cpp
+/pair_harmonic_cut.h
 /pair_lennard_mdf.cpp
 /pair_lennard_mdf.h
 /pair_lj_cut_coul_long_cs.cpp