forked from lijiext/lammps
244 lines
11 KiB
Plaintext
244 lines
11 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 attribute args ... keyword value ... :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 attribute/arg pairs may be appended :l
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attribute = {pair} or {kspace} 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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{kspace} arg = v_name
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v_name = variable with name that calculates scale factor on K-space terms
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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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zero or more keyword/value pairs may be appended :l
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keyword = {scale} or {reset} :l
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{scale} value = {no} or {yes}
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{no} = the variable value is the new setting
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{yes} = the variable value multiplies the original setting
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{reset} value = {no} or {yes}
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{no} = values will remain altered at the end of a run
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{yes} = reset altered values to their original values at the end of a run :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 lj/cut epsilon * * v_scale1 coul/cut scale 3 3 v_scale2 scale yes reset yes
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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 attributes or settings
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over time as a simulation runs. Pair potential and K-space and atom
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attributes which can be varied by this fix are discussed below. Many
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other fixes can also be used to time-vary simulation parameters,
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e.g. the "fix deform" command will change the simulation box
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size/shape and the "fix move" command will change atom positions and
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velocities in a prescribed manner. Also note that many commands allow
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variables as arguments for specific parameters, if described in that
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manner on their doc pages. An equal-style variable can calculate a
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time-dependent quantity, so this is another way to vary a simulation
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parameter over time.
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If {N} is specified as 0, the specified attributes are only changed
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once, before the simulation begins. This is all that is needed if the
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associated variables are not time-dependent. If {N} > 0, then changes
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are made every {N} steps during the simulation, presumably with a
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variable that is time-dependent.
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Depending on the value of the {reset} keyword, attributes changed by
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this fix will or will not be reset back to their original values at
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the end of a simulation. Even if {reset} is specified as {yes}, a
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restart file written during a simulation will contain the modified
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settings.
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If the {scale} keyword is set to {no}, then the value the parameter is
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set to will be whatever the variable generates. If the {scale}
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keyword is set to {yes}, then the value of the altered parameter will
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be the initial value of that parameter multiplied by whatever the
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variable generates. I.e. the variable is now a "scale factor" applied
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in (presumably) a time-varying fashion to the parameter.
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Note that whether scale is {no} or {yes}, internally, the parameters
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themselves are actually altered by this fix. Make sure you use the
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{reset yes} option if you want the parameters to be restored to their
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initial values after the run.
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:line
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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. Note that 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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The {pstyle} argument is the name of the pair style. If "pair_style
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hybrid or hybrid/overlay"_pair_hybrid.html is used, {pstyle} should be
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a sub-style name. For example, {pstyle} could be specified as "soft"
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or "lubricate". The {pparam} argument is the name of the parameter to
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change. This is the current list of pair styles and parameters that
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can be varied by this fix. See the doc pages for individual pair
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styles and their energy formulas for the meaning of these parameters:
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"born"_pair_born.html: a,b,c: type pairs:
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"buck"_pair_buck.html: a,c: type pairs:
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"coul/cut"_pair_coul.html: scale: type pairs:
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"coul/debye"_pair_coul.html: scale: type pairs:
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"coul/long"_pair_coul.html: scale: type pairs:
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"lj/cut"_pair_lj.html: epsilon,sigma: type pairs:
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"lj/expand"_pair_lj_expand.html: epsilon,sigma,delta: type pairs:
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"lubricate"_pair_lubricate.html: mu: global:
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"gauss"_pair_gauss.html: a: type pairs:
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"soft"_pair_soft.html: a: type pairs :tb(c=3,s=:)
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IMPORTANT NOTE: It is easy to add new potentials and their parameters
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to this list. All it typically takes is adding an extract() method to
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the pair_*.cpp file associated with the potential.
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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 atom type pairs within the pair style,
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e.g. the prefactor "a" for "pair_style soft"_pair_soft.html.
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Note that for many of the potentials, the parameter that can be varied
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is effectively a prefactor on the entire energy expression for the
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potential, e.g. the lj/cut epsilon. The parameters listed as "scale"
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are exactly that, since the energy expression for the
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"coul/cut"_pair_coul.html potential (for example) has no labeled
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prefactor in its formula. To apply an effective prefactor to some
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potentials, multiple parameters need to be altered. For example, the
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"Buckingham potential"_pair_buck.html needs both the A and C terms
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altered together. To scale the Buckingham potential, you should thus
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list the pair style twice, once for A and once for C.
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If a type pair parameter is specified, the {I} and {J} settings should
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be specified to indicate which type pairs to apply it to. If a global
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parameter is specified, the {I} and {J} settings still need to be
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specified, but are ignored.
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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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IMPROTANT NOTE: If "pair_style hybrid or
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hybrid/overlay"_pair_hybrid.html is being used, then the {pstyle} will
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be a sub-style name. You must specify I,J arguments that correspond
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to type pair values defined (via the "pair_coeff"_pair_coeff.html
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command) for that sub-style.
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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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:line
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The {kspace} keyword used the specified variable as a scale factor on
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the energy, forces, virial calculated by whatever K-Space solver is
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defined by the "kspace_style"_kspace_style.html command. If the
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variable has a value of 1.0, then the solver is unaltered.
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The {kspace} keyword works this way whether the {scale} keyword
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is set to {no} or {yes}.
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:line
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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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charge = charge on particle
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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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IMPORTANT NOTE: The {atom} keyword works this way whether the {scale}
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keyword is set to {no} or {yes}. I.e. the use of scale yes is not yet
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supported by the {atom} keyword.
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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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:line
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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#howto_15. No parameter of this fix can
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be 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:]
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"compute ti"_compute_ti.html
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[Default:]
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The option defaults are scale = no, reset = no.
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