forked from lijiext/lammps
101 lines
4.0 KiB
HTML
101 lines
4.0 KiB
HTML
<HTML>
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<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</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>minimize command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>minimize tolerance maxiter maxeval
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</PRE>
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<UL><LI>tolerance = stopping tolerance
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<LI>maxiter = max iterations of minimizer
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<LI>maxeval = max number of total force/energy evaluations
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>minimize 1.0e-4 100 1000
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Perform an energy minimization of the system, by adjusting each atom's
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atomic coordinates. The algorithm used is set by the
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<A HREF = "min_style.html">min_style</A> command. Minimize commands can be
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interspersed with <A HREF = "run.html">run</A> commands to alternate between
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relaxation and dynamics. The minimizers are implemented in a robust
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fashion that should allow for systems with highly overlapped atoms
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(large energies and forces) to still be minimized by pushing the atoms
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off of each other.
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</P>
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<P>A minimization involves an outer iteration loop which sets the search
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direction along which coordinates are changed. An inner iteration is
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then performed using a line search algorithm. The line search
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typically evaluates forces and energies several times to set new
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coordinates. The minimization stops if any of several criteria are
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met:
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</P>
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<UL><LI>the change in energy between outer iterations is less than the tolerance
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<LI>the number of outer iterations exceeds maxiter
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<LI>the number of force evaluations exceeds maxeval
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<LI>the 3N dimensional force vector goes (nearly) to zero
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</UL>
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<P>For the first criterion, the specified tolerance is unitless; it is
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met when the ratio of the energy delta to the energy magnitude is
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equal to the tolerance (e.g. one part in 10^4 in the example above).
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</P>
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<P>During a minimization, the outer iteration count is treated as a
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timestep. Output is triggered by this timestep, e.g. thermodynamic
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output or dump and restart files.
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</P>
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<P>For optimal convergence, a <A HREF = "pair_style.html">pair style</A> that goes
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smoothly to 0.0 at the cutoff distance for both energy and force
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should typically be used though this is not required. Examples
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include <I>pair/lj/charmm/coul/charmm</I> and <I>pair/lj/charmm/coul/long</I>.
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If a <I>soft</I> potential is used the Astop value is used for the
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prefactor (no time dependence).
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</P>
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<P>Only fixes that apply force constraints are invoked during
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minimization. The list of the currently implemented ones include fix
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<I>addforce</I>, <I>aveforce</I>, <I>enforce2d</I>, <I>indent</I>, <I>lineforce</I>,
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<I>planeforce</I>, <I>setforce</I>, and <I>wall/lj93</I>. Note that <I>indent</I>,
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<I>wall/lj93</I> have an associated potential energy. If you want that
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energy to be included in the total potential energy of the system (the
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quantity being minimized), you must enable the
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<A HREF = "fix_modify.html">fix_modify</A> <I>energy</I> option for that fix.
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</P>
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<P>Following the minimization a statistical summary is printed that
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includes the energy change and convergence criteria information.
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</P>
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<P><B>Restrictions:</B>
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</P>
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<P>Two features that are not yet implemented listed here, in case someone
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knows how they could be coded:
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</P>
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<P>Two fixes not invoked by a minimization are <A HREF = "fix_shake.html">fix shake</A>
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and <A HREF = "fix_rigid.html">fix rigid</A>. The effect of a fix shake can be
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approximated during a minimization by using stiff spring constants for
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the bonds and/or angles that would normally be constrained by the
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SHAKE algorithm.
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</P>
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<P>The volume of the simulation domain is not allowed to change during a
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minimzation. Ideally we would allow a fix such as <I>npt</I> to impose an
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external pressure that would be included in the minimization
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(i.e. allow the box dimensions to change), but this has not yet been
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implemented.
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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 = "min_style.html">min_style</A>,
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<A HREF = "run_style.html">run_style</A>
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</P>
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<P><B>Default:</B> none
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</P>
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</HTML>
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