forked from lijiext/lammps
77 lines
2.9 KiB
Plaintext
77 lines
2.9 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} or {forcezero}
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backtrack,quadratic,forcezero = 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 selected by the "min_style"_min_style.html 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.
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The {cg} and {sd} 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 {dmax} 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 {quickmin} and {fire} minimization styles, the {dmax} 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 "units"_units.html 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.
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The choice of line search algorithm for the {cg} and {sd} minimization
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styles can be selected via the {line} keyword.
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The default {quadratic} 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 {forcezero}
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line search algorithm is similar to {quadratic}.
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It may be more efficient than {quadratic} on some systems.
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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.
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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 = quadratic.
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