<spanid="index-0"></span><h1>compute msd/nongauss command<aclass="headerlink"href="#compute-msd-nongauss-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>
<divclass="highlight-python"><divclass="highlight"><pre>compute ID group-ID msd/nongauss keyword values ...
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<ulclass="simple">
<li>ID, group-ID are documented in <aclass="reference internal"href="compute.html"><em>compute</em></a> command</li>
<li>msd/nongauss = style name of this compute command</li>
<li>zero or more keyword/value pairs may be appended</li>
<li>keyword = <em>com</em></li>
</ul>
<preclass="literal-block">
<em>com</em> value = <em>yes</em> or <em>no</em>
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<divclass="section"id="examples">
<h2>Examples<aclass="headerlink"href="#examples"title="Permalink to this headline">¶</a></h2>
<divclass="highlight-python"><divclass="highlight"><pre>compute 1 all msd/nongauss
compute 1 upper msd/nongauss com yes
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<divclass="section"id="description">
<h2>Description<aclass="headerlink"href="#description"title="Permalink to this headline">¶</a></h2>
<p>Define a computation that calculates the mean-squared displacement
(MSD) and non-Gaussian parameter (NGP) of the group of atoms,
including all effects due to atoms passing thru periodic boundaries.</p>
<p>A vector of three quantites is calculated by this compute. The first
element of the vector is the total squared dx,dy,dz displacements
drsquared = (dx*dx + dy*dy + dz*dz) of atoms, and the second is the
fourth power of these displacements drfourth = (dx*dx + dy*dy +
dz*dz)*(dx*dx + dy*dy + dz*dz), summed and averaged over atoms in the
group. The 3rd component is the nonGaussian diffusion paramter NGP =
<p>The NGP is a commonly used quantity in studies of dynamical
heterogeneity. Its minimum theoretical value (-0.4) occurs when all
atoms have the same displacement magnitude. NGP=0 for Brownian
diffusion, while NGP > 0 when some mobile atoms move faster than
others.</p>
<p>If the <em>com</em> option is set to <em>yes</em> then the effect of any drift in
the center-of-mass of the group of atoms is subtracted out before the
displacment of each atom is calcluated.</p>
<p>See the <aclass="reference internal"href="compute_msd.html"><em>compute msd</em></a> doc page for further important
NOTEs, which also apply to this compute.</p>
<p><strong>Output info:</strong></p>
<p>This compute calculates a global vector of length 3, which can be
accessed by indices 1-3 by any command that uses global vector values
from a compute as input. See <aclass="reference internal"href="Section_howto.html#howto-15"><span>this section</span></a> for an overview of LAMMPS output
options.</p>
<p>The vector values are “intensive”. The first vector value will be in
distance^2 <aclass="reference internal"href="units.html"><em>units</em></a>, the second is in distance^4 units, and
the 3rd is dimensionless.</p>
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<divclass="section"id="restrictions">
<h2>Restrictions<aclass="headerlink"href="#restrictions"title="Permalink to this headline">¶</a></h2>
<p>This compute is part of the MISC package. It is only 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>
</div>
<divclass="section"id="related-commands">
<h2>Related commands<aclass="headerlink"href="#related-commands"title="Permalink to this headline">¶</a></h2>
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