mirror of https://github.com/lammps/lammps.git
131 lines
4.2 KiB
Plaintext
131 lines
4.2 KiB
Plaintext
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.. index:: fix eos/table
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fix eos/table 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 style file N keyword
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* ID, group-ID are documented in :doc:`fix <fix>` command
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* eos/table = style name of this fix command
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* style = *linear* = method of interpolation
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* file = 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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Examples
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""""""""
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.. parsed-literal::
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fix 1 all eos/table linear eos.table 100000 KEYWORD
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Description
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"""""""""""
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Fix *eos/table* applies a tabulated mesoparticle equation of state to
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relate the particle internal energy (u_i) to the particle internal
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temperature (dpdTheta_i).
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Fix *eos/table* creates interpolation tables of length *N* from
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internal energy values listed in a file as a function of internal
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temperature.
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The interpolation tables are created by fitting cubic splines to the
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file values and interpolating energy values at each of *N* internal
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temperatures, and vice-versa. During a simulation, these tables are
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used to interpolate internal energy or temperature values as needed.
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The interpolation is done with the *linear* style.
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For the *linear* style, the internal temperature is used to find 2
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surrounding table values from which an internal energy is computed by
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linear interpolation, and vice-versa.
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The filename specifies a file containing tabulated internal
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temperature and internal energy values. The keyword specifies a
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section of the file. The format of this file is described below.
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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 (N parameter)
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(blank)
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1 1.00 0.000 (index, internal temperature, internal energy)
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2 1.02 0.001
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...
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500 10.0 0.500
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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. The parameter "N" is
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required and its value is the number of table entries that follow.
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Note that this may be different than the *N* specified in the :doc:`fix eos/table <fix_style>` command. Let Ntable = *N* in the fix
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command, and Nfile = "N" in the tabulated file. What LAMMPS does is a
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preliminary interpolation by creating splines using the Nfile
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tabulated values as nodal points. It uses these to interpolate as
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needed to generate energy and temperature values at Ntable different
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points. The resulting tables of length Ntable are then used as
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described above, when computing energy and temperature relationships.
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This means that if you want the interpolation tables of length Ntable
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to match exactly what is in the tabulated file (with effectively no
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preliminary interpolation), you should set Ntable = Nfile.
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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 is the
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internal energy (in energy units).
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Note that the 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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Restrictions
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""""""""""""
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The fix *eos/table* is only available if LAMMPS is built with the
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USER-DPD package.
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The equation of state must be a monotonically increasing function.
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An exit error will occur if the internal temperature or internal
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energies are not within the table cutoffs.
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Related commands
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""""""""""""""""
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:doc:`fix shardlow <fix_shardlow>`, :doc:`pair dpd/fdt <dpd_fdt>`
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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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