115 lines
4.9 KiB
Plaintext
115 lines
4.9 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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fix_modify command :h3
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[Syntax:]
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fix_modify fix-ID keyword value ... :pre
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fix-ID = ID of the fix to modify :ulb,l
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one or more keyword/value pairs may be appended :l
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keyword = {temp} or {press} or {energy} or {respa} or {dynamic/dof} :l
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{temp} value = compute ID that calculates a temperature
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{press} value = compute ID that calculates a pressure
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{energy} value = {yes} or {no}
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{respa} value = {1} to {max respa level} or {0} (for outermost level)
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{dynamic/dof} value = {yes} or {no}
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yes/no = do or do not recompute the number of degrees of freedom (DOF) contributing to the temperature :pre
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:ule
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[Examples:]
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fix_modify 3 temp myTemp press myPress
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fix_modify 1 energy yes
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fix_modify tether respa 2 :pre
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[Description:]
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Modify one or more parameters of a previously defined fix. Only
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specific fix styles support specific parameters. See the doc pages
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for individual fix commands for info on which ones support which
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fix_modify parameters.
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The {temp} keyword is used to determine how a fix computes
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temperature. The specified compute ID must have been previously
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defined by the user via the "compute"_compute.html command and it must
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be a style of compute that calculates a temperature. All fixes that
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compute temperatures define their own compute by default, as described
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in their documentation. Thus this option allows the user to override
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the default method for computing T.
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The {press} keyword is used to determine how a fix computes pressure.
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The specified compute ID must have been previously defined by the user
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via the "compute"_compute.html command and it must be a style of
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compute that calculates a pressure. All fixes that compute pressures
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define their own compute by default, as described in their
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documentation. Thus this option allows the user to override the
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default method for computing P.
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For fixes that calculate a contribution to the potential energy of the
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system, the {energy} keyword will include that contribution in
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thermodynamic output of potential energy. This is because the {energy
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yes} setting must be specified to include the fix's global or per-atom
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energy in the calculation performed by the "compute
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pe"_compute_pe.html or "compute pe/atom"_compute_pe_atom.html
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commands. See the "thermo_style"_thermo_style.html command for info
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on how potential energy is output. For fixes that tally a global
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energy, it can be printed by using the keyword f_ID in the
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thermo_style custom command, where ID is the fix-ID of the appropriate
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fix.
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NOTE: You must also specify the {energy yes} setting for a fix if you
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are using it when performing an "energy minimization"_minimize.html
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and if you want the energy and forces it produces to be part of the
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optimization criteria.
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For fixes that set or modify forces, it may be possible to select at
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which "r-RESPA"_run_style.html level the fix operates via the {respa}
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keyword. The RESPA level at which the fix is active can be selected.
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This is a number ranging from 1 to the number of levels. If the RESPA
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level is larger than the current maximum, the outermost level will be
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used, which is also the default setting. This default can be restored
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using a value of {0} for the RESPA level. The affected fix has to be
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enabled to support this feature; if not, {fix_modify} will report an
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error. Active fixes with a custom RESPA level setting are reported
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with their specified level at the beginning of a r-RESPA run.
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The {dynamic/dof} keyword determines whether the number of atoms N in
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the fix group and their associated degrees of freedom are re-computed
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each time a temperature is computed. Only fix styles that calculate
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their own internal temperature use this option. Currently this is
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only the "fix rigid/nvt/small"_fix_rigid.html and "fix
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rigid/npt/small"_fix_rigid.html commands for the purpose of
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thermostatting rigid body translation and rotation. By default, N and
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their DOF are assumed to be constant. If you are adding atoms or
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molecules to the system (see the "fix pour"_fix_pour.html, "fix
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deposit"_fix_deposit.html, and "fix gcmc"_fix_gcmc.html commands) or
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expect atoms or molecules to be lost (e.g. due to exiting the
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simulation box or via "fix evaporation"_fix_evaporation.html), then
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this option should be used to insure the temperature is correctly
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normalized.
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NOTE: Other thermostatting fixes, such as "fix nvt"_fix_nh.html, do
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not use the {dynamic/dof} keyword because they use a temperature
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compute to calculate temperature. See the "compute_modify
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dynamic/dof"_compute_modify.html command for a similar way to insure
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correct temperature normalization for those thermostats.
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[Restrictions:] none
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[Related commands:]
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"fix"_fix.html, "compute temp"_compute_temp.html, "compute
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pressure"_compute_pressure.html, "thermo_style"_thermo_style.html
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[Default:]
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The option defaults are temp = ID defined by fix, press = ID defined
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by fix, energy = no, respa = 0.
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