207 lines
7.4 KiB
ReStructuredText
207 lines
7.4 KiB
ReStructuredText
.. 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
|
|
""""""
|
|
|
|
.. code-block:: LAMMPS
|
|
|
|
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
|
|
""""""""
|
|
|
|
.. code-block:: LAMMPS
|
|
|
|
pair_style lj/class2 10.0
|
|
pair_coeff * * 100.0 2.5
|
|
pair_coeff 1 2* 100.0 2.5 9.0
|
|
|
|
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
|
|
|
|
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
|
|
|
|
.. math::
|
|
|
|
E = \epsilon \left[ 2 \left(\frac{\sigma}{r}\right)^9 -
|
|
3 \left(\frac{\sigma}{r}\right)^6 \right]
|
|
\qquad r < r_c
|
|
|
|
:math:`r_c` 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_lj>` pair styles.
|
|
|
|
See :ref:`(Sun) <pair-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 <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, or by mixing as described below:
|
|
|
|
* :math:`\epsilon` (energy units)
|
|
* :math:`\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 :math:`\epsilon` and
|
|
:math:`\sigma` for all class2 potentials is to use the *sixthpower*
|
|
formulas documented by the :doc:`pair_modify <pair_modify>` command.
|
|
The :doc:`pair_modify mix <pair_modify>` setting is thus ignored for
|
|
class2 potentials for epsilon and sigma. However it is still followed
|
|
for mixing the cutoff distance.
|
|
|
|
----------
|
|
|
|
A version of these styles with a soft core, *lj/cut/soft*\ , suitable for use in
|
|
free energy calculations, is part of the USER-FEP package and is documented with
|
|
the :doc:`pair_style */soft <pair_fep_soft>` styles. The version with soft core is
|
|
only available if LAMMPS was built with that package. See the :doc:`Build package <Build_package>` doc page for more info.
|
|
|
|
----------
|
|
|
|
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 on the :doc:`Speed packages <Speed_packages>` doc
|
|
page. 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 :doc:`Build package <Build_package>` doc page for more info.
|
|
|
|
You can specify the accelerated styles explicitly in your input script
|
|
by including their suffix, or you can use the :doc:`-suffix command-line switch <Run_options>` when you invoke LAMMPS, or you can use the
|
|
:doc:`suffix <suffix>` command in your input script.
|
|
|
|
See the :doc:`Speed packages <Speed_packages>` doc page 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 <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 <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 <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 <restart>`, so pair_style and pair_coeff commands do
|
|
not need to be specified in an input script that reads a restart file.
|
|
|
|
Only the *lj/class2* and *lj/class2/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 styles are part of the CLASS2 package. They are only enabled if
|
|
LAMMPS was built with that package. See the :doc:`Build package <Build_package>` doc page for more info.
|
|
|
|
Related commands
|
|
""""""""""""""""
|
|
|
|
:doc:`pair_coeff <pair_coeff>`, :doc:`pair_style */soft <pair_fep_soft>`
|
|
|
|
**Default:** none
|
|
|
|
----------
|
|
|
|
.. _pair-Sun:
|
|
|
|
**(Sun)** Sun, J Phys Chem B 102, 7338-7364 (1998).
|