mirror of https://github.com/lammps/lammps.git
69 lines
2.3 KiB
Plaintext
69 lines
2.3 KiB
Plaintext
"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
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:link(lws,http://lammps.sandia.gov)
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:link(ld,Manual.html)
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:link(lc,Section_commands.html#comm)
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:line
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min_modify command :h3
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[Syntax:]
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min_modify keyword values ... :pre
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one or more keyword/value pairs may be listed :ulb,l
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keyword = {dmax} or {line}
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{dmax} value = max
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max = maximum distance for line search to move (distance units)
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{line} value = {backtrack} or {quadratic}
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backtrack,quadratic = style of linesearch to use :pre
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:ule
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[Examples:]
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min_modify dmax 0.2 :pre
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[Description:]
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This command sets parameters that affect the energy minimization
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algorithms. The various settings may affect the convergence rate and
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overall number of force evaluations required by a minimization, so
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users can experiment with these parameters to tune their
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minimizations.
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The minimization algorithms have an outer iteration (conjugate
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gradient or steepest descent) and an inner iteration which is steps
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along a one-dimensional line search in a particular search direction.
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The {dmax} parameter is how far any atom can move in a single line
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search in any dimension (x, y, or z). Thus a value of 0.1 in real
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"units"_units.html means no atom will move further than 0.1 Angstroms
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in a single outer iteration. This prevents highly overlapped atoms
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from being moved long distances (e.g. through another atom) due to
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large forces.
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The choice of line search algorithm can be selected via the {line}
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keyword. The default backtracking search is very robust and should
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always find a local energy minimum. However, it will "converge" when
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it can no longer reduce the energy of the system. Individual atom
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forces may still be larger than desired at this point, because the
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energy change is measured as the difference of two large values
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(energy before and energy after) and that difference may be smaller
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than machine epsilon even if atoms could move in the gradient
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direction to reduce forces further.
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By contast, the {quadratic} line search algorithm is often able to
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reduce forces closer to 0.0. It may also be more efficient than the
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backtracking algorithm by requiring fewer energy/force evaluations.
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However, it may not be as robust for some problems.
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[Restrictions:] none
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[Related commands:]
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"min_style"_min_style.html, "minimize"_minimize.html
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[Default:]
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The option defaults are dmax = 0.1 and line = backtrack.
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