<spanid="index-0"></span><h1>pair_style eff/cut command<aclass="headerlink"href="#pair-style-eff-cut-command"title="Permalink to this headline">¶</a></h1>
<divclass="section"id="syntax">
<h2>Syntax<aclass="headerlink"href="#syntax"title="Permalink to this headline">¶</a></h2>
<p>The overall electrostatics energy is given in Hartree units of energy
by default and can be modified by an energy-conversion constant,
according to the units chosen (see <aclass="reference internal"href="units.html"><em>electron_units</em></a>). The
cutoff Rc, given in Bohrs (by default), truncates the interaction
distance. The recommended cutoff for this pair style should follow
the minimum image criterion, i.e. half of the minimum unit cell
length.</p>
<p>Style <em>eff/long</em> (not yet available) computes the same interactions as
style <em>eff/cut</em> except that an additional damping factor is applied so
it can be used in conjunction with the
<aclass="reference internal"href="kspace_style.html"><em>kspace_style</em></a> command and its <em>ewald</em> or <em>pppm</em>
option. The Coulombic cutoff specified for this style means that
pairwise interactions within this distance are computed directly;
interactions outside that distance are computed in reciprocal space.</p>
<p>This potential is designed to be used with <aclass="reference internal"href="atom_style.html"><em>atom_style electron</em></a> definitions, in order to handle the
description of systems with interacting nuclei and explicit electrons.</p>
<p>The following coefficients must be defined for each pair of atoms
types via the <aclass="reference internal"href="pair_coeff.html"><em>pair_coeff</em></a> command as in the examples
above, or in the data file or restart files read by the
<aclass="reference internal"href="read_data.html"><em>read_data</em></a> or <aclass="reference internal"href="read_restart.html"><em>read_restart</em></a>
commands, or by mixing as described below:</p>
<ulclass="simple">
<li>cutoff (distance units)</li>
</ul>
<p>For <em>eff/cut</em>, the cutoff coefficient is optional. If it is not used
(as in some of the examples above), the default global value specified
in the pair_style command is used.</p>
<p>For <em>eff/long</em> (not yet available) no cutoff will be specified for an
individual I,J type pair via the <aclass="reference internal"href="pair_coeff.html"><em>pair_coeff</em></a> command.
All type pairs use the same global cutoff specified in the pair_style
command.</p>
<hrclass="docutils"/>
<p>The <em>limit/eradius</em> and <em>pressure/evirials</em> keywrods are optional.
Neither or both must be specified. If not specified they are unset.</p>
<p>The <em>limit/eradius</em> keyword is used to restrain electron size from
becoming excessively diffuse at very high temperatures were the
Gaussian wave packet representation breaks down, and from expanding as
free particles to infinite size. If unset, electron radius is free to
increase without bounds. If set, a restraining harmonic potential of
the form E = 1/2k_ss^2 for s > L_box/2, where k_s = 1 Hartrees/Bohr^2,
is applied on the electron radius.</p>
<p>The <em>pressure/evirials</em> keyword is used to control between two types
of pressure computation: if unset, the computed pressure does not
include the electronic radial virials contributions to the total
pressure (scalar or tensor). If set, the computed pressure will
include the electronic radial virial contributions to the total
pressure (scalar and tensor).</p>
<p>The <em>ecp</em> keyword is used to associate an ECP representation for a
particular atom type. The ECP captures the orbital overlap between a
core pseudo particle and valence electrons within the Pauli repulsion.
A list of type:element-symbol pairs may be provided for all ECP
representations, after the “ecp” keyword.</p>
<divclass="admonition note">
<pclass="first admonition-title">Note</p>
<pclass="last">Default ECP parameters are provided for C, N, O, Al, and Si.
Users can modify these using the pair_coeff command as exemplified
above. For this, the User must distinguish between two different
functional forms supported, one that captures the orbital overlap
assuming the s-type core interacts with an s-like valence electron
(s-s) and another that assumes the interaction is s-p. For systems
that exhibit significant p-character (e.g. C, N, O) the s-p form is
recommended. The “s” ECP form requires 3 parameters and the “p” 5
parameters.</p>
</div>
<divclass="admonition note">
<pclass="first admonition-title">Note</p>
<pclass="last">there are two different pressures that can be reported for eFF
when defining this pair_style, one (default) that considers electrons
do not contribute radial virial components (i.e. electrons treated as
incompressible ‘rigid’ spheres) and one that does. The radial
electronic contributions to the virials are only tallied if the
flexible pressure option is set, and this will affect both global and
per-atom quantities. In principle, the true pressure of a system is
somewhere in between the rigid and the flexible eFF pressures, but,
for most cases, the difference between these two pressures will not be
significant over long-term averaged runs (i.e. even though the energy
partitioning changes, the total energy remains similar).</p>
</div>
<hrclass="docutils"/>
<divclass="admonition note">
<pclass="first admonition-title">Note</p>
<pclass="last">This implemention of eFF gives a reasonably accurate description
for systems containing nuclei from Z = 1-6 in “all electron”
representations. For systems with increasingly non-spherical
electrons, Users should use the ECP representations. ECPs are now
supported and validated for most of the 2nd and 3rd row elements of
the p-block. Predefined parameters are provided for C, N, O, Al, and
Si. The ECP captures the orbital overlap between the core and valence
electrons (i.e. Pauli repulsion) with one of the functional forms:</p>
<p>For atom type pairs I,J and I != J, the cutoff distance for the
<em>eff/cut</em> style can be mixed. The default mix value is <em>geometric</em>.
See the “pair_modify” command for details.</p>
<p>The <aclass="reference internal"href="pair_modify.html"><em>pair_modify</em></a> shift option is not relevant for
these pair styles.</p>
<p>The <em>eff/long</em> (not yet available) style supports the
<aclass="reference internal"href="pair_modify.html"><em>pair_modify</em></a> table option for tabulation of the
short-range portion of the long-range Coulombic interaction.</p>
<p>These pair styles do not support the <aclass="reference internal"href="pair_modify.html"><em>pair_modify</em></a>
tail option for adding long-range tail corrections to energy and
pressure.</p>
<p>These pair styles write their information to <aclass="reference internal"href="restart.html"><em>binary restart files</em></a>, so pair_style and pair_coeff commands do not need
to be specified in an input script that reads a restart file.</p>
<p>These pair styles can only be used via the <em>pair</em> keyword of the
<aclass="reference internal"href="run_style.html"><em>run_style respa</em></a> command. They do not support the
<h2>Restrictions<aclass="headerlink"href="#restrictions"title="Permalink to this headline">¶</a></h2>
<p>These pair styles will only be enabled if LAMMPS is built with the
USER-EFF package. It will only be enabled if LAMMPS was built with
that package. See the <aclass="reference internal"href="Section_start.html#start-3"><span>Making LAMMPS</span></a>
section for more info.</p>
<p>These pair styles require that particles store electron attributes
such as radius, radial velocity, and radital force, as defined by the
<aclass="reference internal"href="atom_style.html"><em>atom_style</em></a>. The <em>electron</em> atom style does all of
this.</p>
<p>Thes pair styles require you to use the <aclass="reference internal"href="comm_modify.html"><em>comm_modify vel yes</em></a> command so that velocites are stored by ghost
atoms.</p>
</div>
<divclass="section"id="related-commands">
<h2>Related commands<aclass="headerlink"href="#related-commands"title="Permalink to this headline">¶</a></h2>
Built with <ahref="http://sphinx-doc.org/">Sphinx</a> using a <ahref="https://github.com/snide/sphinx_rtd_theme">theme</a> provided by <ahref="https://readthedocs.org">Read the Docs</a>.