.. 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 `, 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 ` for a derivation in the context of DVLO theory. :doc:`Pair_style 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 `, 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 ` command as in the examples above, or in the data file or restart files read by the :doc:`read_data ` or :doc:`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 `. 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 ` 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 ` 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 ` when you invoke LAMMPS, or you can use the :doc:`suffix ` command in your input script. See :doc:`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 ` shift option for the energy of the pair interaction. The :doc:`pair_modify ` table option is not relevant for this pair style. This pair style does not support the :doc:`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 `, 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 ` 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 ` 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 ` 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 ` **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