forked from lijiext/lammps
96 lines
3.6 KiB
Plaintext
96 lines
3.6 KiB
Plaintext
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"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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minimize command :h3
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[Syntax:]
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minimize tolerance maxiter maxeval :pre
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tolerance = stopping tolerance
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maxiter = max iterations of minimizer
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maxeval = max number of total force/energy evaluations :ul
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[Examples:]
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minimize 1.0e-4 100 1000 :pre
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[Description:]
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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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"min_style"_min_style.html command. Minimize commands can be
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interspersed with "run"_run.html 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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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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the change in energy between outer iterations is less than the tolerance
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the number of outer iterations exceeds maxiter
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the number of force evaluations exceeds maxeval
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the 3N dimensional force vector goes (nearly) to zero :ul
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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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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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For optimal convergence, a "pair style"_pair_style.html 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 {pair/lj/charmm/coul/charmm} and {pair/lj/charmm/coul/long}.
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If a {soft} potential is used the Astop value is used for the
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prefactor (no time dependence).
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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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{addforce}, {aveforce}, {enforce2d}, {indent}, {lineforce},
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{planeforce}, {setforce}, and {wall/lj93}. Note that {indent},
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{wall/lj93} 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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"fix_modify"_fix_modify.html {energy} option for that fix.
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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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[Restrictions:]
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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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Two fixes not invoked by a minimization are "fix shake"_fix_shake.html
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and "fix rigid"_fix_rigid.html. 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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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 {npt} 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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[Related commands:]
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"min_modify"_min_modify.html, "min_style"_min_style.html,
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"run_style"_run_style.html
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[Default:] none
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