125 lines
3.9 KiB
ReStructuredText
125 lines
3.9 KiB
ReStructuredText
.. index:: pair_style lj/smooth
|
|
.. index:: pair_style lj/smooth/gpu
|
|
.. index:: pair_style lj/smooth/omp
|
|
|
|
pair_style lj/smooth command
|
|
============================
|
|
|
|
Accelerator Variants: *lj/smooth/gpu*, *lj/smooth/omp*
|
|
|
|
Syntax
|
|
""""""
|
|
|
|
.. code-block:: LAMMPS
|
|
|
|
pair_style lj/smooth Rin Rc
|
|
|
|
* Rin = inner cutoff beyond which force smoothing will be applied (distance units)
|
|
* Rc = outer cutoff for lj/smooth interactions (distance units)
|
|
|
|
Examples
|
|
""""""""
|
|
|
|
.. code-block:: LAMMPS
|
|
|
|
pair_style lj/smooth 8.0 10.0
|
|
pair_coeff * * 10.0 1.5
|
|
pair_coeff 1 1 20.0 1.3 7.0 9.0
|
|
|
|
Description
|
|
"""""""""""
|
|
|
|
Style *lj/smooth* computes a LJ interaction with a force smoothing
|
|
applied between the inner and outer cutoff.
|
|
|
|
.. math::
|
|
|
|
E & = 4 \epsilon \left[ \left(\frac{\sigma}{r}\right)^{12} -
|
|
\left(\frac{\sigma}{r}\right)^6 \right]
|
|
\qquad r < r_{in} \\
|
|
F & = C_1 + C_2 (r - r_{in}) + C_3 (r - r_{in})^2 + C_4 (r - r_{in})^3
|
|
\qquad r_{in} < r < r_c
|
|
|
|
The polynomial coefficients C1, C2, C3, C4 are computed by LAMMPS to
|
|
cause the force to vary smoothly from the inner cutoff :math:`r_{in}` to the
|
|
outer cutoff :math:`r_c`.
|
|
|
|
At the inner cutoff the force and its first derivative
|
|
will match the non-smoothed LJ formula. At the outer cutoff the force
|
|
and its first derivative will be 0.0. The inner cutoff cannot be 0.0.
|
|
|
|
.. note::
|
|
|
|
this force smoothing causes the energy to be discontinuous both
|
|
in its values and first derivative. This can lead to poor energy
|
|
conservation and may require the use of a thermostat. Plot the energy
|
|
and force resulting from this formula via the
|
|
:doc:`pair_write <pair_write>` command to see the effect.
|
|
|
|
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)
|
|
* :math:`r_{in}` (distance units)
|
|
* :math:`r_c` (distance units)
|
|
|
|
The last 2 coefficients are optional inner and outer cutoffs. If not
|
|
specified, the global values for :math:`r_{in}` and :math:`r_c` are used.
|
|
|
|
----------
|
|
|
|
.. include:: accel_styles.rst
|
|
|
|
----------
|
|
|
|
Mixing, shift, table, tail correction, restart, rRESPA info
|
|
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
|
|
|
|
For atom type pairs I,J and I != J, the epsilon, sigma, Rin
|
|
coefficients and the cutoff distance for this pair style can be mixed.
|
|
Rin is a cutoff value and is mixed like the cutoff. The other
|
|
coefficients are mixed according to the pair_modify mix option. The
|
|
default mix value is *geometric*\ . See the "pair_modify" command for
|
|
details.
|
|
|
|
This pair style supports the :doc:`pair_modify <pair_modify>` shift
|
|
option for the energy of the pair interaction.
|
|
|
|
The :doc:`pair_modify <pair_modify>` table option is not relevant
|
|
for this pair style.
|
|
|
|
This pair style does not support the :doc:`pair_modify <pair_modify>`
|
|
tail option for adding long-range tail corrections to energy and
|
|
pressure, since the energy of the pair interaction is smoothed to 0.0
|
|
at the cutoff.
|
|
|
|
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 can only be used via the *pair* keyword of the
|
|
:doc:`run_style respa <run_style>` command. It does not support the
|
|
*inner*, *middle*, *outer* keywords.
|
|
|
|
----------
|
|
|
|
Restrictions
|
|
""""""""""""
|
|
|
|
This pair style is part of the EXTRA-PAIR package. It is only enabled if
|
|
LAMMPS was built with that package. See the
|
|
:doc:`Build package <Build_package>` page for more info.
|
|
|
|
Related commands
|
|
""""""""""""""""
|
|
|
|
:doc:`pair_coeff <pair_coeff>`, :doc:`pair lj/smooth/linear <pair_lj_smooth_linear>`
|
|
|
|
Default
|
|
"""""""
|
|
|
|
none
|