forked from lijiext/lammps
154 lines
6.7 KiB
Plaintext
154 lines
6.7 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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fix adapt command :h3
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[Syntax:]
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fix ID group-ID adapt N keyword values ... :pre
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ID, group-ID are documented in "fix"_fix.html command :ulb,l
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adapt = style name of this fix command :l
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N = adapt simulation settings every this many timesteps :l
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one or more keyword/value pairs may be appended :l
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keyword = {pair} or {atom} :l
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{pair} args = pstyle pparam I J v_name
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pstyle = pair style name, e.g. lj/cut
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pparam = parameter to adapt over time
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I,J = type pair(s) to set parameter for
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v_name = variable with name that calculates value of pparam
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{atom} args = aparam v_name
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aparam = parameter to adapt over time
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v_name = variable with name that calculates value of aparam :pre
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:ule
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[Examples:]
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fix 1 all adapt 1 pair soft a 1 1 v_prefactor
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fix 1 all adapt 1 pair soft a 2* 3 v_prefactor
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fix 1 all adapt 1 pair soft a * * v_prefactor soft a 3 3 v_prefactor2
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fix 1 all adapt 10 atom diameter v_size :pre
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[Description:]
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Change or adapt one or more specific simulation settings over time as
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a simulation runs. Pair potential and atom attribute parameters which
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can be varied by this fix are discussed below. Many other fixes can
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also be used to time-vary simulation parameters, e.g. the "fix deform"
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command will change the simulation box size/shape and the "fix move"
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command will change atom positions and velocities in prescribed
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manners.
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IMPORTANT NOTE: Any settings changed by fix adapt are not reset to
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their original values at the end of a simulation. They remain changed
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to the final values they were set to at the end of the run.
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The {pair} keyword enables various parameters of potentials defined by
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the "pair_style"_pair_style.html command to be changed, if the pair
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style supports it. The {pstyle} argument is the name of the pair
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style. If "pair_style hybrid or hybrid/overlay"_pair_hybrid.html is
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used, {pstyle} should be a sub-style name. For example, {pstyle}
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could be specified as "soft" or "lubricate". The {pparam} argument is
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the name of the parameter to change. This is the current list of pair
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styles and parameters that can be varied by this fix. See the doc
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pages for individual pair styles for the meaning of these parameters.
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"soft"_pair_soft.html, a, global,
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"lubricate"_pair_lubricate.html, mu, type pairs :tb(c=3)
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Some parameters are global settings for the pair style, e.g. the
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viscosity setting "mu" for "pair_style lubricate"_pair_lubricate.html.
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Other parameters apply to pairs of atom types within the pair style,
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e.g. the prefactor "a" for "pair_style soft"_pair_soft.html. If a
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type pair parameter is specified, the {I} and {J} settings should be
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specified to indicate which pair(s) to apply it to. Note that in all
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cases, the "pair_style"_pair_style.html and
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"pair_coeff"_pair_coeff.html commands must be used in the usual manner
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to specify these parameters initially; the fix adapt command simply
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overrides the parameters.
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Similar to the "pair_coeff command"_pair_coeff.html, I and J can be
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specified in one of two ways. Explicit numeric values can be used for
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each, as in the 1st example above. I <= J is required. LAMMPS sets
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the coefficients for the symmetric J,I interaction to the same values.
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A wild-card asterisk can be used in place of or in conjunction with
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the I,J arguments to set the coefficients for multiple pairs of atom
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types. This takes the form "*" or "*n" or "n*" or "m*n". If N = the
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number of atom types, then an asterisk with no numeric values means
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all types from 1 to N. A leading asterisk means all types from 1 to n
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(inclusive). A trailing asterisk means all types from n to N
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(inclusive). A middle asterisk means all types from m to n
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(inclusive). Note that only type pairs with I <= J are considered; if
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asterisks imply type pairs where J < I, they are ignored.
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If a global parameter is specified, the {I} and {J} settings still
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need to be specified, but are ignored.
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The {v_name} argument for keyword {pair} is the name of an
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"equal-style variable"_variable.html which will be evaluated each time
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this fix is invoked to set the parameter to a new value. It should be
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specified as v_name, where name is the variable name. Equal-style
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variables can specify formulas with various mathematical functions,
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and include "thermo_style"_thermo_style.html command keywords for the
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simulation box parameters and timestep and elapsed time. Thus it is
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easy to specify parameters that change as a function of time or span
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consecutive runs in a continuous fashion. For the latter, see the
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{start} and {stop} keywords of the "run"_run.html command and the
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{elaplong} keyword of "thermo_style custom"_thermo_style.html for
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details.
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For example, these commands would change the prefactor coefficient of
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the "pair_style soft"_pair_soft.html potential from 10.0 to 30.0 in a
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linear fashion over the course of a simulation:
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variable prefactor equal ramp(10,30)
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fix 1 all adapt 1 pair soft a * * v_prefactor :pre
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The {atom} keyword enables various atom properties to be changed. The
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{aparam} argument is the name of the parameter to change. This is the
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current list of atom parameters that can be varied by this fix:
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diameter = diameter of particle :ul
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The {v_name} argument of the {atom} keyword is the name of an
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"equal-style variable"_variable.html which will be evaluated each time
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this fix is invoked to set the parameter to a new value. It should be
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specified as v_name, where name is the variable name. See the
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discussion above describing the formulas associated with equal-style
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variables. The new value is assigned to the corresponding attribute
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for all atoms in the fix group.
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If the atom parameter is {diameter} and per-atom density and per-atom
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mass are defined for particles (e.g. "atom_style
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granular"_atom_style.html), then the mass of each particle is also
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changed when the diameter changes (density is assumed to stay
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constant).
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For example, these commands would shrink the diameter of all granular
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particles in the "center" group from 1.0 to 0.1 in a linear fashion
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over the course of a 1000-step simulation:
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variable size equal ramp(1.0,0.1)
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fix 1 center adapt 10 atom diameter v_size :pre
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[Restart, fix_modify, output, run start/stop, minimize info:]
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No information about this fix is written to "binary restart
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files"_restart.html. None of the "fix_modify"_fix_modify.html options
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are relevant to this fix. No global or per-atom quantities are stored
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by this fix for access by various "output
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commands"_Section_howto.html#4_15. No parameter of this fix can be
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used with the {start/stop} keywords of the "run"_run.html command.
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This fix is not invoked during "energy minimization"_minimize.html.
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[Restrictions:] none
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[Related commands:] none
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[Default:] none
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