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<li class="toctree-l1"><a class="reference internal" href="Section_intro.html">1. Introduction</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Section_accelerate.html">5. Accelerating LAMMPS performance</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Section_modify.html">10. Modifying & extending LAMMPS</a></li>
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<li>min_modify command</li>
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<div class="section" id="min-modify-command">
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<span id="index-0"></span><h1>min_modify command<a class="headerlink" href="#min-modify-command" title="Permalink to this headline">¶</a></h1>
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<div class="section" id="syntax">
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<h2>Syntax<a class="headerlink" href="#syntax" title="Permalink to this headline">¶</a></h2>
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<div class="highlight-python"><div class="highlight"><pre>min_modify keyword values ...
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</pre></div>
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<ul class="simple">
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<li>one or more keyword/value pairs may be listed</li>
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</ul>
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<pre class="literal-block">
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keyword = <em>dmax</em> or <em>line</em>
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<em>dmax</em> value = max
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max = maximum distance for line search to move (distance units)
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<em>line</em> value = <em>backtrack</em> or <em>quadratic</em> or <em>forcezero</em>
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backtrack,quadratic,forcezero = style of linesearch to use
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</pre>
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</div>
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<div class="section" id="examples">
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<h2>Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
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<div class="highlight-python"><div class="highlight"><pre>min_modify dmax 0.2
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</pre></div>
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</div>
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</div>
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<div class="section" id="description">
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<h2>Description<a class="headerlink" href="#description" title="Permalink to this headline">¶</a></h2>
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<p>This command sets parameters that affect the energy minimization
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algorithms selected by the <a class="reference internal" href="min_style.html"><em>min_style</em></a> command. The
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various settings may affect the convergence rate and overall number of
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force evaluations required by a minimization, so users can experiment
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with these parameters to tune their minimizations.</p>
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<p>The <em>cg</em> and <em>sd</em> minimization styles have an outer iteration and an
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inner iteration which is steps along a one-dimensional line search in
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a particular search direction. The <em>dmax</em> parameter is how far any
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atom can move in a single line search in any dimension (x, y, or z).
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For the <em>quickmin</em> and <em>fire</em> minimization styles, the <em>dmax</em> setting
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is how far any atom can move in a single iteration (timestep). Thus a
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value of 0.1 in real <a class="reference internal" href="units.html"><em>units</em></a> means no atom will move
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further than 0.1 Angstroms in a single outer iteration. This prevents
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highly overlapped atoms from being moved long distances (e.g. through
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another atom) due to large forces.</p>
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<p>The choice of line search algorithm for the <em>cg</em> and <em>sd</em> minimization
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styles can be selected via the <em>line</em> keyword.
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The default <em>quadratic</em> line search algorithm starts out using
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the robust backtracking method described below. However, once
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the system gets close to a local
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minimum and the linesearch steps get small, so that the energy
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is approximately quadratic in the step length, it uses the
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estimated location of zero gradient as the linesearch step,
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provided the energy change is downhill.
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This becomes more efficient than backtracking
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for highly-converged relaxations. The <em>forcezero</em>
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line search algorithm is similar to <em>quadratic</em>.
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It may be more efficient than <em>quadratic</em> on some systems.</p>
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<p>The backtracking search is robust and should always find a local energy
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minimum. However, it will “converge” when it can no longer reduce the
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energy of the system. Individual atom forces may still be larger than
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desired at this point, because the energy change is measured as the
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difference of two large values (energy before and energy after) and
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that difference may be smaller than machine epsilon even if atoms
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could move in the gradient direction to reduce forces further.</p>
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</div>
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<div class="section" id="restrictions">
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<h2>Restrictions<a class="headerlink" href="#restrictions" title="Permalink to this headline">¶</a></h2>
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<blockquote>
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<div>none</div></blockquote>
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</div>
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<div class="section" id="related-commands">
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<h2>Related commands<a class="headerlink" href="#related-commands" title="Permalink to this headline">¶</a></h2>
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<p><a class="reference internal" href="min_style.html"><em>min_style</em></a>, <a class="reference internal" href="minimize.html"><em>minimize</em></a></p>
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</div>
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<div class="section" id="default">
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<h2>Default<a class="headerlink" href="#default" title="Permalink to this headline">¶</a></h2>
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<p>The option defaults are dmax = 0.1 and line = quadratic.</p>
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