<p>If the <em>kspace</em> keyword is set to <em>yes</em>, which is not the default, and
if a <a class="reference internal" href="kspace_style.html"><span class="doc">kspace_style</span></a> is defined, then the interaction
energy will include a Kspace component which is the long-range
Coulombic energy between all the atoms in the first group and all the
atoms in the 2nd group. Likewise, the interaction force calculated by
this compute will include the force on the compute group atoms due to
long-range Coulombic interactions with atoms in the specified group2.</p>
<p>Normally the long-range Coulombic energy converges only when the net
charge of the unit cell is zero. However, one can assume the net
charge of the system is neutralized by a uniform background plasma,
and a correction to the system energy can be applied to reduce
artifacts. For more information see <a class="reference internal" href="#bogusz"><span class="std std-ref">(Bogusz)</span></a>. If the
<em>boundary</em> keyword is set to <em>yes</em>, which is the default, and <em>kspace</em>
contributions are included, then this energy correction term will be
added to the total group-group energy. This correction term does not
affect the force calculation and will be zero if one or both of the
groups are charge neutral. This energy correction term is the same as
that included in the regular Ewald and PPPM routines.</p>
<p>This compute does not calculate any bond or angle or dihedral or
improper interactions between atoms in the two groups.</p>
<hr class="docutils" />
<p>The pairwise contributions to the group-group interactions are
calculated by looping over a neighbor list. The Kspace contribution
to the group-group interactions require essentially the same amount of
work (FFTs, Ewald summation) as computing long-range forces for the
entire system. Thus it can be costly to invoke this compute too
frequently.</p>
<p>If you desire a breakdown of the interactions into a pairwise and
Kspace component, simply invoke the compute twice with the appropriate
yes/no settings for the <em>pair</em> and <em>kspace</em> keywords. This is no more
costly than using a single compute with both keywords set to <em>yes</em>.
The individual contributions can be summed in a
<a class="reference internal" href="variable.html"><span class="doc">variable</span></a> if desired.</p>
<p>This <a class="reference external" href="PDF/kspace.pdf">document</a> describes how the long-range
group-group calculations are performed.</p>
<hr class="docutils" />
<p><strong>Output info:</strong></p>
<p>This compute calculates a global scalar (the energy) and a global
vector of length 3 (force), which can be accessed by indices 1-3.
These values can be used by any command that uses global scalar or
vector values from a compute as input. See <a class="reference internal" href="Section_howto.html#howto-15"><span class="std std-ref">this section</span></a> for an overview of LAMMPS output
options.</p>
<p>Both the scalar and vector values calculated by this compute are
“extensive”. The scalar value will be in energy <a class="reference internal" href="units.html"><span class="doc">units</span></a>.
The vector values will be in force <a class="reference internal" href="units.html"><span class="doc">units</span></a>.</p>
</div>
<div class="section" id="restrictions">
<h2>Restrictions</h2>
<p>Not all pair styles can be evaluated in a pairwise mode as required by
this compute. For example, 3-body and other many-body potentials,
such as <a class="reference internal" href="pair_tersoff.html"><span class="doc">Tersoff</span></a> and
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