137 lines
4.3 KiB
Plaintext
137 lines
4.3 KiB
Plaintext
.. index:: pair_style exp6/rx
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pair_style exp6/rx 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 exp6/rx cutoff
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* cutoff = global cutoff for DPD interactions (distance units)
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Examples
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""""""""
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.. parsed-literal::
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pair_style exp6/rx 10.0
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pair_coeff * * exp6.params h2o h2o 1.0 1.0 10.0
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pair_coeff * * exp6.params h2o 1fluid 1.0 1.0 10.0
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pair_coeff * * exp6.params 1fluid 1fluid 1.0 1.0 10.0
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Description
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"""""""""""
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Style *exp6/rx* is used in reaction DPD simulations, where the coarse-grained (CG)
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particles are composed of *m* species whose reaction rate kinetics are determined
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from a set of *n* reaction rate equations through the :doc:`fix rx <fix_rx>` command.
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The species of one CG particle can interact with a species in a neighboring CG
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particle through a site-site interaction potential model. The *exp6/rx* style
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computes an exponential-6 potential given by
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.. image:: Eqs/pair_exp6_rx.jpg
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:align: center
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where the *epsilon* parameter determines the depth of the potential
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minimum located at *Rm*\ , and *alpha* determines the softness of the repulsion.
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The coefficients must be defined for each species in a given particle type
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via the :doc:`pair_coeff <pair_coeff>` command as in the examples above, where
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the first argument is the filename that includes the exponential-6 parameters
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for each species. The file includes the species tag followed by the *alpha*\ ,
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*epsilon* and *Rm* parameters. The format of the file is described below.
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The second and third arguments specify the site-site interaction
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potential between two species contained within two different particles.
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The species tags must either correspond to the species defined in the reaction
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kinetics files specified with the :doc:`fix rx <fix_rx>` command
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or they must correspond to the tag "1fluid", signifying interaction
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with a product species mixture determined through a one-fluid approximation.
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The interaction potential is weighted by the geometric average of the
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concentrations of the two species. The coarse-grained potential is
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stored before and after the reaction kinetics solver is applied, where the
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difference is defined to be the internal chemical energy (uChem).
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The fourth and fifth arguments specify the *Rm* and *epsilon* scaling exponents.
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The final argument specifies the interaction cutoff.
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----------
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The format of a tabulated file is as follows (without the parenthesized comments):
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.. parsed-literal::
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# exponential-6 parameters for various species (one or more comment or blank lines)
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.. parsed-literal::
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h2o exp6 11.00 0.02 3.50 (species, exp6, alpha, Rm, epsilon)
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no2 exp6 13.60 0.01 3.70
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...
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co2 exp6 13.00 0.03 3.20
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A section begins with a non-blank line whose 1st character is not a
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"#"; blank lines or lines starting with "#" can be used as comments
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between sections.
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Following a blank line, the next N lines list the species and their
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corresponding parameters. The first argument is the species tag,
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the second argument is the exp6 tag, the 3rd argument is the *alpha*
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parameter (energy units), the 4th argument is the *epsilon* parameter
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(energy-distance^6 units), and the 5th argument is the *Rm*
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parameter (distance units). If a species tag of "1fluid" is listed as a
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pair coefficient, a one-fluid approximation is specified where a
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concentration-dependent combination of the parameters is computed
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through the following equations:
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.. image:: Eqs/pair_exp6_rx_oneFluid.jpg
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:align: center
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where
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.. image:: Eqs/pair_exp6_rx_oneFluid2.jpg
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:align: center
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and xa and xb are the mole fractions of a and b, respectively, which
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comprise the gas mixture.
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----------
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**Mixing, shift, table, tail correction, restart, rRESPA info**\ :
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This pair style does not support mixing. Thus, coefficients for all
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I,J pairs must be specified explicitly.
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This style does not support the :doc:`pair_modify <pair_modify>` shift option
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for the energy of the exp() and 1/r^6 portion of the pair interaction.
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This style does not support the pair_modify tail option for adding long-range
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tail corrections to energy and pressure for the A,C terms in the
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pair interaction.
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Restrictions
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""""""""""""
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None
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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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.. _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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