2009-03-19 01:37:50 +08:00
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<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A>
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<HR>
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<H3>fix evaporate command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>fix ID group-ID evaporate N M region-ID seed
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</PRE>
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2010-05-07 01:32:58 +08:00
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<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
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<LI>evaporate = style name of this fix command
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<LI>N = delete atoms every this many timesteps
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<LI>M = number of atoms to delete each time
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<LI>region-ID = ID of region within which to perform deletions
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2009-03-19 01:37:50 +08:00
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<LI>seed = random number seed to use for choosing atoms to delete
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2010-05-07 01:32:58 +08:00
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<LI>zero or more keyword/value pairs may be appended
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2010-05-07 02:00:32 +08:00
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<PRE>keyword = <I>molecule</I>
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<I>molecule</I> value = <I>no</I> or <I>yes</I>
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2010-05-07 01:32:58 +08:00
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</PRE>
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2009-03-19 01:37:50 +08:00
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</UL>
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<P><B>Examples:</B>
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</P>
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2010-05-07 01:32:58 +08:00
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<PRE>fix 1 solvent evaporate 1000 10 surface 49892
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fix 1 solvent evaporate 1000 10 surface 38277 molecule yes
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2009-03-19 01:37:50 +08:00
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Remove M atoms from the simulation every N steps. This can be used,
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2010-05-07 01:32:58 +08:00
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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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2009-03-19 01:53:44 +08:00
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</P>
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2010-05-07 01:32:58 +08:00
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<P>If the setting for the <I>molecule</I> keyword is <I>no</I>, 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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</P>
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<P>If the setting for the <I>molecule</I> keyword is <I>yes</I>, 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. If the molecule ID of the chosen atom is 0, then it is
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assumed to not be part of a molecule, and just the single atom is
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deleted.
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</P>
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<P>As an example, if you wish to delete 10 water molecules every <I>N</I>
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steps, you should set <I>M</I> 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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2009-03-19 01:37:50 +08:00
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</P>
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<P>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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</P>
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<P><B>Restart, fix_modify, output, run start/stop, minimize info:</B>
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</P>
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<P>No information about this fix is written to <A HREF = "restart.html">binary restart
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files</A>. None of the <A HREF = "fix_modify.html">fix_modify</A> options
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are relevant to this fix.
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</P>
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2010-04-03 00:51:06 +08:00
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<P>This fix computes a global scalar, which can be accessed by various
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<A HREF = "Section_howto.html#4_15">output commands</A>. 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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2009-03-19 01:37:50 +08:00
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</P>
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<P>No parameter of this fix can be used with the <I>start/stop</I> keywords of
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the <A HREF = "run.html">run</A> command. This fix is not invoked during <A HREF = "minimize.html">energy
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minimization</A>.
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</P>
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<P><B>Restrictions:</B> none
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</P>
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<P><B>Related commands:</B>
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</P>
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<P><A HREF = "fix_deposit.html">fix deposit</A>
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</P>
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2010-05-07 01:32:58 +08:00
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<P><B>Default:</B>
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</P>
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<P>The option defaults are molecule = no.
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2009-03-19 01:37:50 +08:00
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</P>
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</HTML>
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