forked from lijiext/lammps
180 lines
5.6 KiB
Plaintext
180 lines
5.6 KiB
Plaintext
.. index:: pair_style yukawa/colloid
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pair_style yukawa/colloid command
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=================================
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pair_style yukawa/colloid/gpu command
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=====================================
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pair_style yukawa/colloid/omp command
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=====================================
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Syntax
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""""""
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.. parsed-literal::
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pair_style yukawa/colloid kappa cutoff
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* kappa = screening length (inverse distance units)
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* cutoff = global cutoff for colloidal Yukawa interactions (distance units)
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Examples
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""""""""
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.. parsed-literal::
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pair_style yukawa/colloid 2.0 2.5
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pair_coeff 1 1 100.0 2.3
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pair_coeff * * 100.0
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Description
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"""""""""""
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Style *yukawa/colloid* computes pairwise interactions with the formula
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.. image:: Eqs/pair_yukawa_colloid.jpg
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:align: center
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where Ri and Rj are the radii of the two particles and Rc is the
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cutoff.
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In contrast to :doc:`pair_style yukawa <pair_yukawa>`, this functional
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form arises from the Coulombic interaction between two colloid
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particles, screened due to the presence of an electrolyte, see the
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book by :ref:`Safran <Safran>` for a derivation in the context of DVLO
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theory. :doc:`Pair_style yukawa <pair_yukawa>` is a screened Coulombic
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potential between two point-charges and uses no such approximation.
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This potential applies to nearby particle pairs for which the Derjagin
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approximation holds, meaning h << Ri + Rj, where h is the
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surface-to-surface separation of the two particles.
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When used in combination with :doc:`pair_style colloid <pair_colloid>`,
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the two terms become the so-called DLVO potential, which combines
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electrostatic repulsion and van der Waals attraction.
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The following coefficients must be defined for each pair of atoms
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types via the :doc:`pair_coeff <pair_coeff>` command as in the examples
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above, or in the data file or restart files read by the
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:doc:`read_data <read_data>` or :doc:`read_restart <read_restart>`
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commands, or by mixing as described below:
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* A (energy/distance units)
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* cutoff (distance units)
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The prefactor A is determined from the relationship between surface
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charge and surface potential due to the presence of electrolyte. Note
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that the A for this potential style has different units than the A
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used in :doc:`pair_style yukawa <pair_yukawa>`. For low surface
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potentials, i.e. less than about 25 mV, A can be written as:
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.. parsed-literal::
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A = 2 * PI * R*eps*eps0 * kappa * psi^2
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where
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* R = colloid radius (distance units)
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* eps0 = permittivity of free space (charge^2/energy/distance units)
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* eps = relative permittivity of fluid medium (dimensionless)
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* kappa = inverse screening length (1/distance units)
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* psi = surface potential (energy/charge units)
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The last coefficient is optional. If not specified, the global
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yukawa/colloid cutoff is used.
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----------
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Styles with a *gpu*\ , *intel*\ , *kk*\ , *omp*\ , or *opt* suffix are
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functionally the same as the corresponding style without the suffix.
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They have been optimized to run faster, depending on your available
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hardware, as discussed in :doc:`Section_accelerate <Section_accelerate>`
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of the manual. The accelerated styles take the same arguments and
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should produce the same results, except for round-off and precision
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issues.
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These accelerated styles are part of the GPU, USER-INTEL, KOKKOS,
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USER-OMP and OPT packages, respectively. They are only enabled if
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LAMMPS was built with those packages. See the :ref:`Making LAMMPS <start_3>` section for more info.
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You can specify the accelerated styles explicitly in your input script
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by including their suffix, or you can use the :ref:`-suffix command-line switch <start_7>` when you invoke LAMMPS, or you can
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use the :doc:`suffix <suffix>` command in your input script.
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See :doc:`Section_accelerate <Section_accelerate>` of the manual for
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more instructions on how to use the accelerated styles effectively.
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----------
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**Mixing, shift, table, tail correction, restart, rRESPA info**\ :
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For atom type pairs I,J and I != J, the A coefficient and cutoff
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distance for this pair style can be mixed. A is an energy value mixed
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like a LJ epsilon. The default mix value is *geometric*\ . See the
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"pair_modify" command for details.
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This pair style supports the :doc:`pair_modify <pair_modify>` shift
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option for the energy of the pair interaction.
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The :doc:`pair_modify <pair_modify>` table option is not relevant
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for this pair style.
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This pair style does not support the :doc:`pair_modify <pair_modify>`
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tail option for adding long-range tail corrections to energy and
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pressure.
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This pair style writes its information to :doc:`binary restart files <restart>`, so pair_style and pair_coeff commands do not need
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to be specified in an input script that reads a restart file.
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This pair style can only be used via the *pair* keyword of the
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:doc:`run_style respa <run_style>` command. It does not support the
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*inner*\ , *middle*\ , *outer* keywords.
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----------
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Restrictions
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""""""""""""
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This style is part of the COLLOID package. It is only enabled if
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LAMMPS was built with that package. See the :ref:`Making LAMMPS <start_3>` section for more info.
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This pair style requires that atoms be finite-size spheres with a
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diameter, as defined by the :doc:`atom_style sphere <atom_style>`
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command.
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Per-particle polydispersity is not yet supported by this pair style;
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per-type polydispersity is allowed. This means all particles of the
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same type must have the same diameter. Each type can have a different
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diameter.
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Related commands
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""""""""""""""""
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:doc:`pair_coeff <pair_coeff>`
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**Default:** none
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----------
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.. _Safran:
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**(Safran)** Safran, Statistical Thermodynamics of Surfaces, Interfaces,
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And Membranes, Westview Press, ISBN: 978-0813340791 (2003).
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.. _lws: http://lammps.sandia.gov
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.. _ld: Manual.html
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.. _lc: Section_commands.html#comm
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