forked from lijiext/lammps
230 lines
7.8 KiB
Plaintext
230 lines
7.8 KiB
Plaintext
.. index:: pair_style colloid
|
|
|
|
pair_style colloid command
|
|
==========================
|
|
|
|
pair_style colloid/gpu command
|
|
==============================
|
|
|
|
pair_style colloid/omp command
|
|
==============================
|
|
|
|
Syntax
|
|
""""""
|
|
|
|
.. parsed-literal::
|
|
|
|
pair_style colloid cutoff
|
|
|
|
* cutoff = global cutoff for colloidal interactions (distance units)
|
|
|
|
Examples
|
|
""""""""
|
|
|
|
.. parsed-literal::
|
|
|
|
pair_style colloid 10.0
|
|
pair_coeff * * 25 1.0 10.0 10.0
|
|
pair_coeff 1 1 144 1.0 0.0 0.0 3.0
|
|
pair_coeff 1 2 75.398 1.0 0.0 10.0 9.0
|
|
pair_coeff 2 2 39.478 1.0 10.0 10.0 25.0
|
|
|
|
Description
|
|
"""""""""""
|
|
|
|
Style *colloid* computes pairwise interactions between large colloidal
|
|
particles and small solvent particles using 3 formulas. A colloidal
|
|
particle has a size > sigma; a solvent particle is the usual
|
|
Lennard-Jones particle of size sigma.
|
|
|
|
The colloid-colloid interaction energy is given by
|
|
|
|
.. image:: Eqs/pair_colloid_cc.jpg
|
|
:align: center
|
|
|
|
where A_cc is the Hamaker constant, a1 and a2 are the radii of the two
|
|
colloidal particles, and Rc is the cutoff. This equation results from
|
|
describing each colloidal particle as an integrated collection of
|
|
Lennard-Jones particles of size sigma and is derived in
|
|
:ref:`(Everaers) <Everaers>`.
|
|
|
|
The colloid-solvent interaction energy is given by
|
|
|
|
.. image:: Eqs/pair_colloid_cs.jpg
|
|
:align: center
|
|
|
|
where A_cs is the Hamaker constant, a is the radius of the colloidal
|
|
particle, and Rc is the cutoff. This formula is derived from the
|
|
colloid-colloid interaction, letting one of the particle sizes go to
|
|
zero.
|
|
|
|
The solvent-solvent interaction energy is given by the usual
|
|
Lennard-Jones formula
|
|
|
|
.. image:: Eqs/pair_colloid_ss.jpg
|
|
:align: center
|
|
|
|
with A_ss set appropriately, which results from letting both particle
|
|
sizes go to zero.
|
|
|
|
When used in combination with :doc:`pair_style yukawa/colloid <pair_colloid>`, the two terms become the so-called
|
|
DLVO potential, which combines electrostatic repulsion and van der
|
|
Waals attraction.
|
|
|
|
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:
|
|
|
|
* A (energy units)
|
|
* sigma (distance units)
|
|
* d1 (distance units)
|
|
* d2 (distance units)
|
|
* cutoff (distance units)
|
|
|
|
A is the Hamaker energy prefactor and should typically be set as
|
|
follows:
|
|
|
|
* A_cc = colloid/colloid = 4 pi^2 = 39.5
|
|
* A_cs = colloid/solvent = sqrt(A_cc*A_ss)
|
|
* A_ss = solvent/solvent = 144 (assuming epsilon = 1, so that 144/36 = 4)
|
|
|
|
Sigma is the size of the solvent particle or the constituent particles
|
|
integrated over in the colloidal particle and should typically be set
|
|
as follows:
|
|
|
|
* Sigma_cc = colloid/colloid = 1.0
|
|
* Sigma_cs = colloid/solvent = arithmetic mixing between colloid sigma and solvent sigma
|
|
* Sigma_ss = solvent/solvent = 1.0 or whatever size the solvent particle is
|
|
|
|
Thus typically Sigma_cs = 1.0, unless the solvent particle's size !=
|
|
1.0.
|
|
|
|
D1 and d2 are particle diameters, so that d1 = 2*a1 and d2 = 2*a2 in
|
|
the formulas above. Both d1 and d2 must be values >= 0. If d1 > 0
|
|
and d2 > 0, then the pair interacts via the colloid-colloid formula
|
|
above. If d1 = 0 and d2 = 0, then the pair interacts via the
|
|
solvent-solvent formula. I.e. a d value of 0 is a Lennard-Jones
|
|
particle of size sigma. If either d1 = 0 or d2 = 0 and the other is
|
|
larger, then the pair interacts via the colloid-solvent formula.
|
|
|
|
Note that the diameter of a particular particle type may appear in
|
|
multiple pair_coeff commands, as it interacts with other particle
|
|
types. You should insure the particle diameter is specified
|
|
consistently each time it appears.
|
|
|
|
The last coefficient is optional. If not specified, the global cutoff
|
|
specified in the pair_style command is used. However, you typically
|
|
want different cutoffs for interactions between different particle
|
|
sizes. E.g. if colloidal particles of diameter 10 are used with
|
|
solvent particles of diameter 1, then a solvent-solvent cutoff of 2.5
|
|
would correspond to a colloid-colloid cutoff of 25. A good
|
|
rule-of-thumb is to use a colloid-solvent cutoff that is half the big
|
|
diameter + 4 times the small diameter. I.e. 9 = 5 + 4 for the
|
|
colloid-solvent cutoff in this case.
|
|
|
|
.. note::
|
|
|
|
When using pair_style colloid for a mixture with 2 (or more)
|
|
widely different particles sizes (e.g. sigma=10 colloids in a
|
|
background sigma=1 LJ fluid), you will likely want to use these
|
|
commands for efficiency: :doc:`neighbor multi <neighbor>` and
|
|
:doc:`comm_modify multi <comm_modify>`.
|
|
|
|
|
|
----------
|
|
|
|
|
|
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 <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 <start_3>` 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 <start_7>` when you invoke LAMMPS, or you can
|
|
use the :doc:`suffix <suffix>` command in your input script.
|
|
|
|
See :doc:`Section_accelerate <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 A, sigma, d1, and d2
|
|
coefficients and cutoff distance for this pair style can be mixed. A
|
|
is an energy value mixed like a LJ epsilon. D1 and d2 are distance
|
|
values and are mixed like sigma. 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.
|
|
|
|
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 style is part of the COLLOID package. It is only enabled if
|
|
LAMMPS was built with that package. See the :ref:`Making LAMMPS <start_3>` section for more info.
|
|
|
|
Normally, this pair style should be used with finite-size particles
|
|
which have a diameter, e.g. see the :doc:`atom_style sphere <atom_style>` command. However, this is not a requirement,
|
|
since the only definition of particle size is via the pair_coeff
|
|
parameters for each type. In other words, the physical radius of the
|
|
particle is ignored. Thus you should insure that the d1,d2 parameters
|
|
you specify are consistent with the physical size of the particles of
|
|
that type.
|
|
|
|
Per-particle polydispersity is not yet supported by this pair style;
|
|
only per-type polydispersity is enabled via the pair_coeff parameters.
|
|
|
|
Related commands
|
|
""""""""""""""""
|
|
|
|
:doc:`pair_coeff <pair_coeff>`
|
|
|
|
**Default:** none
|
|
|
|
|
|
----------
|
|
|
|
|
|
.. _Everaers:
|
|
|
|
|
|
|
|
**(Everaers)** Everaers, Ejtehadi, Phys Rev E, 67, 041710 (2003).
|
|
|
|
|
|
.. _lws: http://lammps.sandia.gov
|
|
.. _ld: Manual.html
|
|
.. _lc: Section_commands.html#comm
|