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105 lines
4.0 KiB
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<HTML>
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<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Page</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A>
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<HR>
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<H3>min_style command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>min_style style
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</PRE>
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<UL><LI>style = <I>cg</I> or <I>hftn</I> or <I>sd</I> or <I>quickmin</I> or <I>fire</I>
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>min_style cg
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min_style fire
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Choose a minimization algorithm to use when a <A HREF = "minimize.html">minimize</A>
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command is performed.
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</P>
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<P>Style <I>cg</I> is the Polak-Ribiere version of the conjugate gradient (CG)
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algorithm. At each iteration the force gradient is combined with the
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previous iteration information to compute a new search direction
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perpendicular (conjugate) to the previous search direction. The PR
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variant affects how the direction is chosen and how the CG method is
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restarted when it ceases to make progress. The PR variant is thought
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to be the most effective CG choice for most problems.
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</P>
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<P>Style <I>hftn</I> is a Hessian-free truncated Newton algorithm. At each
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iteration a quadratic model of the energy potential is solved by a
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conjugate gradient inner iteration. The Hessian (second derivatives)
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of the energy is not formed directly, but approximated in each
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conjugate search direction by a finite difference directional
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derivative. When close to an energy minimum, the algorithm behaves
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like a Newton method and exhibits a quadratic convergence rate to high
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accuracy. In most cases the behavior of <I>hftn</I> is similar to <I>cg</I>,
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but it offers an alternative if <I>cg</I> seems to perform poorly. This
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style is not affected by the <A HREF = "min_modify.html">min_modify</A> command.
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</P>
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<P>Style <I>sd</I> is a steepest descent algorithm. At each iteration, the
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search direction is set to the downhill direction corresponding to the
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force vector (negative gradient of energy). Typically, steepest
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descent will not converge as quickly as CG, but may be more robust in
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some situations.
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</P>
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<P>Style <I>quickmin</I> is a damped dynamics method described in
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<A HREF = "#Sheppard">(Sheppard)</A>, where the damping parameter is related to the
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projection of the velocity vector along the current force vector for
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each atom. The velocity of each atom is initialized to 0.0 by this
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style, at the beginning of a minimization.
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</P>
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<P>Style <I>fire</I> is a damped dynamics method described in
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<A HREF = "#Bitzek">(Bitzek)</A>, which is similar to <I>quickmin</I> but adds a variable
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timestep and alters the projection operation to maintain components of
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the velocity non-parallel to the current force vector. The velocity
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of each atom is initialized to 0.0 by this style, at the beginning of
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a minimization.
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</P>
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<P>Either the <I>quickmin</I> and <I>fire</I> styles are useful in the context of
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nudged elastic band (NEB) calculations via the <A HREF = "neb.html">neb</A> command.
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</P>
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<P>IMPORTANT NOTE: The damped dynamic minimizers use whatever timestep
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you have defined via the <A HREF = "timestep.html">timestep</A> command. Often they
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will converge more quickly if you use a timestep about 10x larger than
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you would normally use for dynamics simulations.
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</P>
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<P>IMPORTANT NOTE: The <I>quickmin</I> and <I>fire</I> styles do not yet support
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the use of the <A HREF = "fix_box_relax.html">fix box/relax</A> command or
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minimizations involving the electron radius in <A HREF = "pair_eff.html">eFF</A>
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models.
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</P>
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<P><B>Restrictions:</B> none
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</P>
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<P><B>Related commands:</B>
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</P>
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<P><A HREF = "min_modify.html">min_modify</A>, <A HREF = "minimize.html">minimize</A>, <A HREF = "neb.html">neb</A>
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</P>
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<P><B>Default:</B>
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</P>
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<PRE>min_style cg
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</PRE>
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<HR>
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<A NAME = "Sheppard"></A>
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<P><B>(Sheppard)</B> Sheppard, Terrell, Henkelman, J Chem Phys, 128, 134106
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(2008). See ref 1 in this paper for original reference to Qmin in
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Jonsson, Mills, Jacobsen.
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</P>
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<A NAME = "Bitzek"></A>
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<P><B>(Bitzek)</B> Bitzek, Koskinen, Gahler, Moseler, Gumbsch, Phys Rev Lett,
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97, 170201 (2006).
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</P>
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</HTML>
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