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			<div class="section" id="pair-style-table-rx-command">
			<span id="index-0"></span><h1>pair_style table/rx command</h1>
			<div class="section" id="syntax">
			<h2>Syntax</h2>
			<pre class="literal-block">
			pair_style table style N
			</pre>
			<p>style = <em>lookup</em> or <em>linear</em> or <em>spline</em> or <em>bitmap</em> = method of interpolation
			N = use N values in <em>lookup</em>, <em>linear</em>, <em>spline</em> tables
			N = use 2^N values in <em>bitmap</em> tables</p>
			</div>
			<div class="section" id="examples">
			<h2>Examples</h2>
			<pre class="literal-block">
			pair_style table/rx linear 1000
			pair_style table/rx bitmap 12
			pair_coeff * * rxn.table ENTRY1 h2o h2o 10.0
			pair_coeff * * rxn.table ENTRY1 1fluid 1fluid 10.0
			pair_coeff * 3 rxn.table ENTRY1 h2o no2 10.0
			</pre>
			</div>
			<div class="section" id="description">
			<h2>Description</h2>
			<p>Style <em>table/rx</em> is used in reaction DPD simulations,where the
			coarse-grained (CG) particles are composed of <em>m</em> species whose
			reaction rate kinetics are determined from a set of <em>n</em> reaction rate
			equations through the <a class="reference internal" href="fix_rx.html"><span class="doc">fix rx</span></a> command. The species of
			one CG particle can interact with a species in a neighboring CG
			particle through a site-site interaction potential model. Style
			<em>table/rx</em> creates interpolation tables of length <em>N</em> from pair
			potential and force values listed in a file(s) as a function of
			distance. The files are read by the <a class="reference internal" href="pair_coeff.html"><span class="doc">pair_coeff</span></a>
			command.</p>
			<p>The interpolation tables are created by fitting cubic splines to the
			file values and interpolating energy and force values at each of <em>N</em>
			distances. During a simulation, these tables are used to interpolate
			energy and force values as needed. The interpolation is done in one
			of 4 styles: <em>lookup</em>, <em>linear</em>, <em>spline</em>, or <em>bitmap</em>.</p>
			<p>For the <em>lookup</em> style, the distance between 2 atoms is used to find
			the nearest table entry, which is the energy or force.</p>
			<p>For the <em>linear</em> style, the pair distance is used to find 2
			surrounding table values from which an energy or force is computed by
			linear interpolation.</p>
			<p>For the <em>spline</em> style, a cubic spline coefficients are computed and
			stored at each of the <em>N</em> values in the table. The pair distance is
			used to find the appropriate set of coefficients which are used to
			evaluate a cubic polynomial which computes the energy or force.</p>
			<p>For the <em>bitmap</em> style, the N means to create interpolation tables
			that are 2^N in length. The pair distance is used to index into the
			table via a fast bit-mapping technique <a class="reference internal" href="#wolff"><span class="std std-ref">(Wolff)</span></a> and a linear
			interpolation is performed between adjacent table values.</p>
			<p>The following coefficients must be defined for each pair of atoms
			types via the <a class="reference internal" href="pair_coeff.html"><span class="doc">pair_coeff</span></a> command as in the examples
			above.</p>
			<ul class="simple">
			<li>filename</li>
			<li>keyword</li>
			<li>species1</li>
			<li>species2</li>
			<li>cutoff (distance units)</li>
			</ul>
			<p>The filename specifies a file containing tabulated energy and force
			values. The keyword specifies a section of the file. The cutoff is
			an optional coefficient. If not specified, the outer cutoff in the
			table itself (see below) will be used to build an interpolation table
			that extend to the largest tabulated distance. If specified, only
			file values up to the cutoff are used to create the interpolation
			table. The format of this file is described below.</p>
			<p>The species tags define the site-site interaction potential between
			two species contained within two different particles. The species
			tags must either correspond to the species defined in the reaction
			kinetics files specified with the <a class="reference internal" href="fix_rx.html"><span class="doc">fix rx</span></a> command or they
			must correspond to the tag “1fluid”, signifying interaction with a
			product species mixture determined through a one-fluid approximation.
			The interaction potential is weighted by the geometric average of the
			concentrations of the two species. The coarse-grained potential is
			stored before and after the reaction kinetics solver is applied, where
			the difference is defined to be the internal chemical energy (uChem).</p>
			<hr class="docutils" />
			<p>Here are some guidelines for using the pair_style table/rx command to
			best effect:</p>
			<ul class="simple">
			<li>Vary the number of table points; you may need to use more than you think
			to get good resolution.</li>
			<li>Always use the <a class="reference internal" href="pair_write.html"><span class="doc">pair_write</span></a> command to produce a plot
			of what the final interpolated potential looks like. This can show up
			interpolation “features” you may not like.</li>
			<li>Start with the linear style; it’s the style least likely to have problems.</li>
			<li>Use <em>N</em> in the pair_style command equal to the “N” in the tabulation
			file, and use the “RSQ” or “BITMAP” parameter, so additional interpolation
			is not needed. See discussion below.</li>
			<li>Make sure that your tabulated forces and tabulated energies are consistent
			(dE/dr = -F) along the entire range of r values.</li>
			<li>Use as large an inner cutoff as possible. This avoids fitting splines
			to very steep parts of the potential.</li>
			</ul>
			<hr class="docutils" />
			<p>The format of a tabulated file is a series of one or more sections,
			defined as follows (without the parenthesized comments):</p>
			<div class="highlight-default"><div class="highlight"><pre><span></span><span class="c1"># Morse potential for Fe (one or more comment or blank lines)</span>
			</pre></div>
			</div>
			<pre class="literal-block">
			MORSE_FE (keyword is first text on line)
			N 500 R 1.0 10.0 (N, R, RSQ, BITMAP, FPRIME parameters)
			(blank)
			1 1.0 25.5 102.34 (index, r, energy, force)
			2 1.02 23.4 98.5
			...
			500 10.0 0.001 0.003
			</pre>
			<p>A section begins with a non-blank line whose 1st character is not a
			“#”; blank lines or lines starting with “#” can be used as comments
			between sections. The first line begins with a keyword which
			identifies the section. The line can contain additional text, but the
			initial text must match the argument specified in the pair_coeff
			command. The next line lists (in any order) one or more parameters
			for the table. Each parameter is a keyword followed by one or more
			numeric values.</p>
			<p>The parameter “N” is required and its value is the number of table
			entries that follow. Note that this may be different than the <em>N</em>
			specified in the <a class="reference internal" href="pair_style.html"><span class="doc">pair_style table/rx</span></a> command. Let
			Ntable = <em>N</em> in the pair_style command, and Nfile = “N” in the
			tabulated file. What LAMMPS does is a preliminary interpolation by
			creating splines using the Nfile tabulated values as nodal points. It
			uses these to interpolate as needed to generate energy and force
			values at Ntable different points. The resulting tables of length
			Ntable are then used as described above, when computing energy and
			force for individual pair distances. This means that if you want the
			interpolation tables of length Ntable to match exactly what is in the
			tabulated file (with effectively no preliminary interpolation), you
			should set Ntable = Nfile, and use the “RSQ” or “BITMAP” parameter.
			The internal table abscissa is RSQ (separation distance squared).</p>
			<p>All other parameters are optional. If “R” or “RSQ” or “BITMAP” does
			not appear, then the distances in each line of the table are used
			as-is to perform spline interpolation. In this case, the table values
			can be spaced in <em>r</em> uniformly or however you wish to position table
			values in regions of large gradients.</p>
			<p>If used, the parameters “R” or “RSQ” are followed by 2 values <em>rlo</em>
			and <em>rhi</em>. If specified, the distance associated with each energy and
			force value is computed from these 2 values (at high accuracy), rather
			than using the (low-accuracy) value listed in each line of the table.
			The distance values in the table file are ignored in this case.
			For “R”, distances uniformly spaced between <em>rlo</em> and <em>rhi</em> are
			computed; for “RSQ”, squared distances uniformly spaced between
			<em>rlorlo</em> and <em>rhirhi</em> are computed.</p>
			<p>If used, the parameter “BITMAP” is also followed by 2 values <em>rlo</em> and
			<em>rhi</em>. These values, along with the “N” value determine the ordering
			of the N lines that follow and what distance is associated with each.
			This ordering is complex, so it is not documented here, since this
			file is typically produced by the <a class="reference internal" href="pair_write.html"><span class="doc">pair_write</span></a> command
			with its <em>bitmap</em> option. When the table is in BITMAP format, the “N”
			parameter in the file must be equal to 2^M where M is the value
			specified in the pair_style command. Also, a cutoff parameter cannot
			be used as an optional 3rd argument in the pair_coeff command; the
			entire table extent as specified in the file must be used.</p>
			<p>If used, the parameter “FPRIME” is followed by 2 values <em>fplo</em> and
			<em>fphi</em> which are the derivative of the force at the innermost and
			outermost distances listed in the table. These values are needed by
			the spline construction routines. If not specified by the “FPRIME”
			parameter, they are estimated (less accurately) by the first 2 and
			last 2 force values in the table. This parameter is not used by
			BITMAP tables.</p>
			<p>Following a blank line, the next N lines list the tabulated values.
			On each line, the 1st value is the index from 1 to N, the 2nd value is
			r (in distance units), the 3rd value is the energy (in energy units),
			and the 4th is the force (in force units). The r values must increase
			from one line to the next (unless the BITMAP parameter is specified).</p>
			<p>Note that one file can contain many sections, each with a tabulated
			potential. LAMMPS reads the file section by section until it finds
			one that matches the specified keyword.</p>
			<hr class="docutils" />
			<p><strong>Mixing, shift, table, tail correction, restart, rRESPA info</strong>:</p>
			<p>This pair style does not support mixing. Thus, coefficients for all
			I,J pairs must be specified explicitly.</p>
			<p>The <a class="reference internal" href="pair_modify.html"><span class="doc">pair_modify</span></a> shift, table, and tail options are
			not relevant for this pair style.</p>
			<p>This pair style writes the settings for the “pair_style table/rx” command
			to <a class="reference internal" href="restart.html"><span class="doc">binary restart files</span></a>, so a pair_style command does
			not need to specified in an input script that reads a restart file.
			However, the coefficient information is not stored in the restart
			file, since it is tabulated in the potential files. Thus, pair_coeff
			commands do need to be specified in the restart input script.</p>
			<p>This pair style can only be used via the <em>pair</em> keyword of the
			<a class="reference internal" href="run_style.html"><span class="doc">run_style respa</span></a> command. It does not support the
			<em>inner</em>, <em>middle</em>, <em>outer</em> keywords.</p>
			</div>
			<hr class="docutils" />
			<div class="section" id="restrictions">
			<h2>Restrictions</h2>
			<p>This command is part of the USER-DPD package. It is only enabled if
			LAMMPS was built with that package. See the <a class="reference internal" href="Section_start.html#start-3"><span class="std std-ref">Making LAMMPS</span></a> section for more info.</p>
			</div>
			<div class="section" id="related-commands">
			<h2>Related commands</h2>
			<p><a class="reference internal" href="pair_coeff.html"><span class="doc">pair_coeff</span></a></p>
			<p><strong>Default:</strong> none</p>
			<hr class="docutils" />
			<p id="wolff"><strong>(Wolff)</strong> Wolff and Rudd, Comp Phys Comm, 120, 200-32 (1999).</p>
			</div>
			</div>


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