<span id="index-0"></span><h1>pair_style hybrid command<a class="headerlink" href="#pair-style-hybrid-command" title="Permalink to this headline">¶</a></h1>
<h1>pair_style hybrid/overlay/omp command<a class="headerlink" href="#pair-style-hybrid-overlay-omp-command" title="Permalink to this headline">¶</a></h1>
<div class="section" id="syntax">
<h2>Syntax<a class="headerlink" href="#syntax" title="Permalink to this headline">¶</a></h2>
<p>If an assignment to <em>none</em> is made in a simulation with the
<em>hybrid/overlay</em> pair style, it wipes out all previous assignments of
that atom type pair to sub-styles.</p>
<p>Note that you may need to use an <a class="reference internal" href="atom_style.html"><em>atom_style</em></a> hybrid
command in your input script, if atoms in the simulation will need
attributes from several atom styles, due to using multiple pair
potentials.</p>
<hr class="docutils" />
<p>Different force fields (e.g. CHARMM vs AMBER) may have different rules
for applying weightings that change the strength of pairwise
interactions bewteen pairs of atoms that are also 1-2, 1-3, and 1-4
neighbors in the molecular bond topology, as normally set by the
<a class="reference internal" href="special_bonds.html"><em>special_bonds</em></a> command. Different weights can be
assigned to different pair hybrid sub-styles via the <a class="reference internal" href="pair_modify.html"><em>pair_modify special</em></a> command. This allows multiple force fields
to be used in a model of a hybrid system. See the
<a class="reference internal" href="pair_modify.html"><em>pair_modify</em></a> doc page for details.</p>
<p>The potential energy contribution to the overall system due to an
individual sub-style can be accessed and output via the <a class="reference internal" href="compute_pair.html"><em>compute pair</em></a> command.</p>
<hr class="docutils" />
<p>IMPORTANT: Several of the potentials defined via the pair_style
command in LAMMPS are really many-body potentials, such as Tersoff,
AIREBO, MEAM, ReaxFF, etc. The way to think about using these
potentials in a hybrid setting is as follows.</p>
<p>A subset of atom types is assigned to the many-body potential with a
single <a class="reference internal" href="pair_coeff.html"><em>pair_coeff</em></a> command, using “* <a href="#id1"><span class="problematic" id="id2">*</span></a>” to include
all types and the NULL keywords described above to exclude specific
types not assigned to that potential. If types 1,3,4 were assigned in
that way (but not type 2), this means that all many-body interactions
between all atoms of types 1,3,4 will be computed by that potential.
Pair_style hybrid allows interactions between type pairs 2-2, 1-2,
2-3, 2-4 to be specified for computation by other pair styles. You
could even add a second interaction for 1-1 to be computed by another
pair style, assuming pair_style hybrid/overlay is used.</p>
<p>But you should not, as a general rule, attempt to exclude the
many-body interactions for some subset of the type pairs within the
set of 1,3,4 interactions, e.g. exclude 1-1 or 1-3 interactions. That
is not conceptually well-defined for many-body interactions, since the
potential will typically calculate energies and foces for small groups
of atoms, e.g. 3 or 4 atoms, using the neighbor lists of the atoms to
find the additional atoms in the group. It is typically non-physical
to think of excluding an interaction between a particular pair of
atoms when the potential computes 3-body or 4-body interactions.</p>
<p>However, you can still use the pair_coeff none setting or the
<a class="reference internal" href="neigh_modify.html"><em>neigh_modify exclude</em></a> command to exclude certain
type pairs from the neighbor list that will be passed to a manybody
sub-style. This will alter the calculations made by a many-body
potential, since it builds its list of 3-body, 4-body, etc
interactions from the pair list. You will need to think carefully as
to whether it produces a physically meaningful result for your model.</p>
<p>For example, imagine you have two atom types in your model, type 1 for
atoms in one surface, and type 2 for atoms in the other, and you wish
to use a Tersoff potential to compute interactions within each
surface, but not between surfaces. Then either of these two command
<p>Note that to prevent the Tersoff potential from computing C/C
interactions, you would need to modify the SiC.tersoff file to turn
off C/C interaction, i.e. by setting the appropriate coefficients to
0.0.</p>
<hr class="docutils" />
<p>Styles with a <em>cuda</em>, <em>gpu</em>, <em>intel</em>, <em>kk</em>, <em>omp</em>, or <em>opt</em> suffix are
functionally the same as the corresponding style without the suffix.
They have been optimized to run faster, depending on your available
hardware, as discussed in <a class="reference internal" href="Section_accelerate.html"><em>Section_accelerate</em></a>
of the manual.</p>
<p>Since the <em>hybrid</em> and <em>hybrid/overlay</em> styles delegate computation
to the individual sub-styles, the suffix versions of the <em>hybrid</em>
and <em>hybrid/overlay</em> styles are used to propagate the corresponding
suffix to all sub-styles, if those versions exist. Otherwise the
non-accelerated version will be used.</p>
<p>The individual accelerated sub-styles are part of the USER-CUDA, GPU,
USER-OMP and OPT packages, respectively. They are only enabled if
LAMMPS was built with those packages. See the
<a class="reference internal" href="Section_start.html#start-3"><span>Making LAMMPS</span></a> section for more info.</p>
<p>You can specify the accelerated styles explicitly in your input script
by including their suffix, or you can use the <a class="reference internal" href="Section_start.html#start-7"><span>-suffix command-line switch</span></a> when you invoke LAMMPS, or you can
use the <a class="reference internal" href="suffix.html"><em>suffix</em></a> command in your input script.</p>
<p>See <a class="reference internal" href="Section_accelerate.html"><em>Section_accelerate</em></a> of the manual for
more instructions on how to use the accelerated styles effectively.</p>
<a class="reference internal" href="pair_modify.html"><em>pair_modify</em></a> command are passed along to all
sub-styles of the hybrid potential.</p>
<p>For atom type pairs I,J and I != J, if the sub-style assigned to I,I
and J,J is the same, and if the sub-style allows for mixing, then the
coefficients for I,J can be mixed. This means you do not have to
specify a pair_coeff command for I,J since the I,J type pair will be
assigned automatically to the sub-style defined for both I,I and J,J
and its coefficients generated by the mixing rule used by that
sub-style. For the <em>hybrid/overlay</em> style, there is an additional
requirement that both the I,I and J,J pairs are assigned to a single
sub-style. See the “pair_modify” command for details of mixing rules.
See the See the doc page for the sub-style to see if allows for
mixing.</p>
<p>The hybrid pair styles supports the <a class="reference internal" href="pair_modify.html"><em>pair_modify</em></a>
shift, table, and tail options for an I,J pair interaction, if the
associated sub-style supports it.</p>
<p>For the hybrid pair styles, the list of sub-styles and their
respective settings are written to <a class="reference internal" href="restart.html"><em>binary restart files</em></a>, so a <a class="reference internal" href="pair_style.html"><em>pair_style</em></a> 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. Thus, pair_coeff commands need to be re-specified in the
restart input script.</p>
<p>These pair styles support the use of the <em>inner</em>, <em>middle</em>, and
<em>outer</em> keywords of the <a class="reference internal" href="run_style.html"><em>run_style respa</em></a> command, if
their sub-styles do.</p>
</div>
<div class="section" id="restrictions">
<h2>Restrictions<a class="headerlink" href="#restrictions" title="Permalink to this headline">¶</a></h2>
<p>When using a long-range Coulombic solver (via the
<a class="reference internal" href="kspace_style.html"><em>kspace_style</em></a> command) with a hybrid pair_style,
one or more sub-styles will be of the “long” variety,
e.g. <em>lj/cut/coul/long</em> or <em>buck/coul/long</em>. You must insure that the
short-range Coulombic cutoff used by each of these long pair styles is
the same or else LAMMPS will generate an error.</p>
</div>
<div class="section" id="related-commands">
<h2>Related commands<a class="headerlink" href="#related-commands" title="Permalink to this headline">¶</a></h2>
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