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pair_yukawa_colloid.txt
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.. index:: pair_style yukawa/colloid
pair_style yukawa/colloid command
=================================
pair_style yukawa/colloid/gpu command
=====================================
pair_style yukawa/colloid/omp command
=====================================
Syntax
""""""
.. parsed-literal::
pair_style yukawa/colloid kappa cutoff
* kappa = screening length (inverse distance units)
* cutoff = global cutoff for colloidal Yukawa interactions (distance units)
Examples
""""""""
.. parsed-literal::
pair_style yukawa/colloid 2.0 2.5
pair_coeff 1 1 100.0 2.3
pair_coeff * * 100.0
Description
"""""""""""
Style *yukawa/colloid* computes pairwise interactions with the formula
.. image:: Eqs/pair_yukawa_colloid.jpg
:align: center
where Ri and Rj are the radii of the two particles and Rc is the
cutoff.
In contrast to :doc:`pair_style yukawa <pair_yukawa>`, this functional
form arises from the Coulombic interaction between two colloid
particles, screened due to the presence of an electrolyte, see the
book by :ref:`Safran <Safran>` for a derivation in the context of DVLO
theory. :doc:`Pair_style yukawa <pair_yukawa>` is a screened Coulombic
potential between two point-charges and uses no such approximation.
This potential applies to nearby particle pairs for which the Derjagin
approximation holds, meaning h << Ri + Rj, where h is the
surface-to-surface separation of the two particles.
When used in combination with :doc:`pair_style 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/distance units)
* cutoff (distance units)
The prefactor A is determined from the relationship between surface
charge and surface potential due to the presence of electrolyte. Note
that the A for this potential style has different units than the A
used in :doc:`pair_style yukawa <pair_yukawa>`. For low surface
potentials, i.e. less than about 25 mV, A can be written as:
.. parsed-literal::
A = 2 * PI * R*eps*eps0 * kappa * psi^2
where
* R = colloid radius (distance units)
* eps0 = permittivity of free space (charge^2/energy/distance units)
* eps = relative permittivity of fluid medium (dimensionless)
* kappa = inverse screening length (1/distance units)
* psi = surface potential (energy/charge units)
The last coefficient is optional. If not specified, the global
yukawa/colloid cutoff is used.
----------
Styles with a *cuda*, *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 USER-CUDA, 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 coefficient and cutoff
distance for this pair style can be mixed. A is an energy value mixed
like a LJ epsilon. 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.
This pair style requires that atoms be finite-size spheres with a
diameter, as defined by the :doc:`atom_style sphere <atom_style>`
command.
Per-particle polydispersity is not yet supported by this pair style;
per-type polydispersity is allowed. This means all particles of the
same type must have the same diameter. Each type can have a different
diameter.
Related commands
""""""""""""""""
:doc:`pair_coeff <pair_coeff>`
**Default:** none
----------
.. _Safran:
**(Safran)** Safran, Statistical Thermodynamics of Surfaces, Interfaces,
And Membranes, Westview Press, ISBN: 978-0813340791 (2003).
.. _lws: http://lammps.sandia.gov
.. _ld: Manual.html
.. _lc: Section_commands.html#comm
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