forked from lijiext/lammps
92 lines
3.4 KiB
Plaintext
92 lines
3.4 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 evaporate command :h3
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[Syntax:]
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fix ID group-ID evaporate N M region-ID seed :pre
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ID, group-ID are documented in "fix"_fix.html command :ulb,l
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evaporate = style name of this fix command :l
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N = delete atoms every this many timesteps :l
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M = number of atoms to delete each time :l
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region-ID = ID of region within which to perform deletions :l
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seed = random number seed to use for choosing atoms to delete :l
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zero or more keyword/value pairs may be appended :l
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keyword = {molecule}
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{molecule} value = {no} or {yes} :pre
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:ule
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[Examples:]
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fix 1 solvent evaporate 1000 10 surface 49892
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fix 1 solvent evaporate 1000 10 surface 38277 molecule yes :pre
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[Description:]
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Remove M atoms from the simulation every N steps. This can be used,
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for example, to model evaporation of solvent particles or moleclues
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(i.e. drying) of a system. Every N steps, the number of atoms in the
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fix group and within the specifed region are counted. M of these are
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chosen at random and deleted. If there are less than M eligible
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particles, then all of them are deleted.
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If the setting for the {molecule} keyword is {no}, then only single
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atoms are deleted. In this case, you should insure you do not delete
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only a portion of a molecule (only some of its atoms), or LAMMPS will
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soon generate an error when it tries to find those atoms. LAMMPS will
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warn you if any of the atoms eligible for deletion have a non-zero
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molecule ID, but does not check for this at the time of deletion.
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If the setting for the {molecule} keyword is {yes}, then when an atom
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is chosen for deletion, the entire molecule it is part of is deleted.
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The count of deleted atoms is incremented by the number of atoms in
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the molecule, which may make it exceed {M}. If the molecule ID of the
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chosen atom is 0, then it is assumed to not be part of a molecule, and
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just the single atom is deleted.
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As an example, if you wish to delete 10 water molecules every {N}
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steps, you should set {M} to 30. If only the water's oxygen atoms
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were in the fix group, then two hydrogen atoms would be deleted when
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an oxygen atom is selected for deletion, whether the hydrogens are
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inside the evaporation region or not.
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Note that neighbor lists are re-built on timesteps that atoms are
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removed. Thus you should not remove atoms too frequently or you will
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incur overhead due to the cost of building neighbor lists.
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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.
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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 number of deleted atoms. The scalar value calculated by
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this fix is "intensive".
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No parameter of this fix can be used with the {start/stop} keywords of
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the "run"_run.html command. This fix is not invoked during "energy
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minimization"_minimize.html.
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[Restrictions:]
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This fix is part of the MISC package. It is only enabled if LAMMPS
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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 deposit"_fix_deposit.html
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[Default:]
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The option defaults are molecule = no.
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