forked from lijiext/lammps
170 lines
5.4 KiB
Plaintext
170 lines
5.4 KiB
Plaintext
.. index:: fix eos/table/rx
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fix eos/table/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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fix ID group-ID eos/table/rx style file1 N keyword file2
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* ID, group-ID are documented in :doc:`fix <fix>` command
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* eos/table/rx = style name of this fix command
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* style = *linear* = method of interpolation
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* file1 = filename containing the tabulated equation of state
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* N = use N values in *linear* tables
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* keyword = name of table keyword correponding to table file
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* file2 = filename containing the heats of formation of each species
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Examples
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""""""""
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.. parsed-literal::
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fix 1 all eos/table/rx linear eos.table 10000 KEYWORD thermo.table
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Description
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"""""""""""
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Fix *eos/table/rx* applies a tabulated mesoparticle equation
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of state to relate the concentration-dependent particle internal
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energy (u_i) to the particle internal temperature (dpdTheta_i).
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The concentration-dependent particle internal energy (u_i) is
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computed according to the following relation:
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.. image:: Eqs/fix_eos_table_rx.jpg
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:align: center
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where *m* is the number of species, *c_i,j* is the concentration of
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species *j* in particle *i*\ , *u_j* is the internal energy of species j,
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*DeltaH_f,j* is the heat of formation of species *j*\ , N is the number of
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molecules represented by the coarse-grained particle, kb is the
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Boltzmann constant, and T is the temperature of the system.
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Fix *eos/table/rx* creates interpolation tables of length *N* from *m*
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internal energy values of each species *u_j* listed in a file as a
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function of internal temperature. During a simulation, these tables
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are used to interpolate internal energy or temperature values as needed.
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The interpolation is done with the *linear* style. For the *linear* style,
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the internal temperature is used to find 2 surrounding table values from
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which an internal energy is computed by linear interpolation. A secant
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solver is used to determine the internal temperature from the internal energy.
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The first filename specifies a file containing tabulated internal
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temperature and *m* internal energy values for each species *u_j*\ .
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The keyword specifies a section of the file. The format of this
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file is described below.
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The second filename specifies a file containing heat of formation
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*DeltaH_f,j* for each species.
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----------
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The format of a tabulated file is as follows (without the
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parenthesized comments):
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.. parsed-literal::
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# EOS TABLE (one or more comment or blank lines)
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.. parsed-literal::
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KEYWORD (keyword is first text on line)
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N 500 h2 no2 n2 ... no (N parameter species1 species2 ... speciesN)
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(blank)
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1 1.00 0.000 ... 0.0000 (index, internal temperature, internal energy of species 1, ..., internal energy of species m)
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2 1.02 0.001 ... 0.0002
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...
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500 10.0 0.500 ... 1.0000
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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. The first line begins with a keyword which
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identifies the section. The line can contain additional text, but the
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initial text must match the argument specified in the fix command.
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The next line lists the number of table entries and the species names
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that correspond with all the species listed in the reaction equations
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through the *fix rx* command.
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The parameter "N" is required and its value is the number of table
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entries that follow. Let Nfile = "N" in the tabulated file.
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What LAMMPS does is a preliminary interpolation by creating splines
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using the Nfile tabulated values as nodal points.
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Following a blank line, the next N lines list the tabulated values.
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On each line, the 1st value is the index from 1 to N, the 2nd value is
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the internal temperature (in temperature units), the 3rd value until
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the *m+3* value are the internal energies of the m species (in energy units).
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Note that all internal temperature and internal energy values must
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increase from one line to the next.
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Note that one file can contain many sections, each with a tabulated
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potential. LAMMPS reads the file section by section until it finds
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one that matches the specified keyword.
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----------
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The format of a heat of formation file is as follows (without the
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parenthesized comments):
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.. parsed-literal::
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# HEAT OF FORMATION TABLE (one or more comment or blank lines)
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.. parsed-literal::
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(blank)
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h2 0.00 (species name, heat of formation)
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no2 0.34
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n2 0.00
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...
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no 0.93
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Note that the species can be listed in any order. The tag that is
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used as the species name must correspond with the tags used to define
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the reactions with the :doc:`fix rx <fix_rx>` command.
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----------
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Restrictions
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""""""""""""
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This command is part of the USER-DPD 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 command also requires use of the :doc:`atom_style dpd <atom_style>`
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command.
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The equation of state must be a monotonically increasing function.
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An error will occur if the internal temperature or internal energies
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are not within the table cutoffs.
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Related commands
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""""""""""""""""
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:doc:`fix rx <fix_rx>`,
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:doc:`pair dpd/fdt <dpd_fdt>`
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**Default:** none
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----------
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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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