forked from lijiext/lammps
114 lines
4.1 KiB
Plaintext
114 lines
4.1 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 langevin/eff command :h3
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[Syntax:]
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fix ID group-ID langevin/eff Tstart Tstop damp seed keyword values ... :pre
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ID, group-ID are documented in "fix"_fix.html command :ulb,l
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langevin/eff = style name of this fix command :l
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Tstart,Tstop = desired temperature at start/end of run (temperature units) :l
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damp = damping parameter (time units) :l
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seed = random number seed to use for white noise (positive integer) :l
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zero or more keyword/value pairs may be appended :l
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keyword = {scale} or {tally} or {zero}
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{scale} values = type ratio
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type = atom type (1-N)
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ratio = factor by which to scale the damping coefficient
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{tally} values = {no} or {yes}
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{no} = do not tally the energy added/subtracted to atoms
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{yes} = do tally the energy added/subtracted to atoms :pre
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{zero} value = {no} or {yes}
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{no} = do not set total random force to zero
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{yes} = set total random force to zero :pre
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:ule
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[Examples:]
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fix 3 boundary langevin/eff 1.0 1.0 10.0 699483
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fix 1 all langevin/eff 1.0 1.1 10.0 48279 scale 3 1.5 :pre
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[Description:]
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Apply a Langevin thermostat as described in "(Schneider)"_#Schneider
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to a group of nuclei and electrons in the "electron force
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field"_pair_eff.html model. Used with "fix nve/eff"_fix_nve_eff.html,
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this command performs Brownian dynamics (BD), since the total force on
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each atom will have the form:
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F = Fc + Ff + Fr
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Ff = - (m / damp) v
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Fr is proportional to sqrt(Kb T m / (dt damp)) :pre
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Fc is the conservative force computed via the usual inter-particle
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interactions ("pair_style"_pair_style.html).
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The Ff and Fr terms are added by this fix on a per-particle basis.
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The operation of this fix is exactly like that described by the "fix
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langevin"_fix_langevin.html command, except that the thermostatting
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is also applied to the radial electron velocity for electron
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particles.
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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. Because the state of the random number generator
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is not saved in restart files, this means you cannot do "exact"
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restarts with this fix, where the simulation continues on the same as
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if no restart had taken place. However, in a statistical sense, a
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restarted simulation should produce the same behavior.
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The "fix_modify"_fix_modify.html {temp} option is supported by this
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fix. You can use it to assign a temperature "compute"_compute.html
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you have defined to this fix which will be used in its thermostatting
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procedure, as described above. For consistency, the group used by
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this fix and by the compute should be the same.
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The "fix_modify"_fix_modify.html {energy} option is supported by this
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fix to add the energy change induced by Langevin thermostatting to the
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system's potential energy as part of "thermodynamic
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output"_thermo_style.html. Note that use of this option requires
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setting the {tally} keyword to {yes}.
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This fix computes a global scalar which can be accessed by various
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"output commands"_Section_howto.html#howto_15. The scalar is the
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cummulative energy change due to this fix. The scalar value
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calculated by this fix is "extensive". Note that calculation of this
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quantity requires setting the {tally} keyword to {yes}.
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This fix can ramp its target temperature over multiple runs, using the
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{start} and {stop} keywords of the "run"_run.html command. See the
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"run"_run.html command for details of how to do this.
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This fix is not invoked during "energy minimization"_minimize.html.
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[Restrictions:] none
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This fix is part of the USER-EFF package. It is only enabled if
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LAMMPS was built with that package. See the "Making
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LAMMPS"_Section_start.html#start_3 section for more info.
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[Related commands:]
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"fix langevin"_fix_langevin.html
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[Default:]
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The option defaults are scale = 1.0 for all types and tally = no.
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:line
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:link(Dunweg)
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[(Dunweg)] Dunweg and Paul, Int J of Modern Physics C, 2, 817-27 (1991).
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:link(Schneider)
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[(Schneider)] Schneider and Stoll, Phys Rev B, 17, 1302 (1978).
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