forked from lijiext/lammps
90 lines
2.9 KiB
Plaintext
90 lines
2.9 KiB
Plaintext
.. index:: pair_write
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pair_write 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_write itype jtype N style inner outer file keyword Qi Qj
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* itype,jtype = 2 atom types
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* N = # of values
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* style = *r* or *rsq* or *bitmap*
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* inner,outer = inner and outer cutoff (distance units)
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* file = name of file to write values to
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* keyword = section name in file for this set of tabulated values
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* Qi,Qj = 2 atom charges (charge units) (optional)
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Examples
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""""""""
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.. parsed-literal::
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pair_write 1 3 500 r 1.0 10.0 table.txt LJ
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pair_write 1 1 1000 rsq 2.0 8.0 table.txt Yukawa_1_1 -0.5 0.5
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Description
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"""""""""""
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Write energy and force values to a file as a function of distance for
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the currently defined pair potential. This is useful for plotting the
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potential function or otherwise debugging its values. If the file
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already exists, the table of values is appended to the end of the file
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to allow multiple tables of energy and force to be included in one
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file.
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The energy and force values are computed at distances from inner to
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outer for 2 interacting atoms of type itype and jtype, using the
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appropriate :doc:`pair_coeff <pair_coeff>` coefficients. If the style
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is *r*\ , then N distances are used, evenly spaced in r; if the style is
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*rsq*\ , N distances are used, evenly spaced in r^2.
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For example, for N = 7, style = *r*\ , inner = 1.0, and outer = 4.0,
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values are computed at r = 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0.
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If the style is *bitmap*\ , then 2^N values are written to the file in a
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format and order consistent with how they are read in by the
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:doc:`pair_coeff <pair_coeff>` command for pair style *table*\ . For
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reasonable accuracy in a bitmapped table, choose N >= 12, an *inner*
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value that is smaller than the distance of closest approach of 2
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atoms, and an *outer* value <= cutoff of the potential.
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If the pair potential is computed between charged atoms, the charges
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of the pair of interacting atoms can optionally be specified. If not
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specified, values of Qi = Qj = 1.0 are used.
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The file is written in the format used as input for the
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:doc:`pair_style <pair_style>` *table* option with *keyword* as the
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section name. Each line written to the file lists an index number
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(1-N), a distance (in distance units), an energy (in energy units),
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and a force (in force units).
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Restrictions
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""""""""""""
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All force field coefficients for pair and other kinds of interactions
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must be set before this command can be invoked.
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Due to how the pairwise force is computed, an inner value > 0.0 must
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be specified even if the potential has a finite value at r = 0.0.
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For EAM potentials, the pair_write command only tabulates the
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pairwise portion of the potential, not the embedding portion.
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Related commands
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""""""""""""""""
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:doc:`pair_style table <pair_table>`,
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:doc:`pair_style <pair_style>`, :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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