2006-09-22 00:22:34 +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>mass command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>mass I value
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</PRE>
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2008-03-01 09:13:20 +08:00
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<UL><LI>I = atom type (see asterisk form below)
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2006-09-22 00:22:34 +08:00
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<LI>value = mass
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>mass 1 1.0
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mass * 62.5
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mass 2* 62.5
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Set the mass for all atoms of one or more atom types. Mass values can
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also be set in the <A HREF = "read_data.html">read_data</A> data file. See the
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<A HREF = "units.html">units</A> command for what mass units to use.
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</P>
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2008-07-25 07:46:15 +08:00
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<P>Most atom styles require per-type masses to be specified. One
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exception is <A HREF = "atom_style.html">atom_style granular</A> or <A HREF = "atom_style.html">atom_style
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peri</A>, where masses are defined for individual atoms,
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not types. These are defined in the file read by the
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<A HREF = "read_data.html">read_data</A> command, or set to default values by the
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<A HREF = "create_atoms.html">create_atoms</A> command, or set to new values by the
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<A HREF = "set.html">set density</A> command. Also note that <A HREF = "pair_eam.html">pair_style
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eam</A> defines the masses of atom types in the EAM
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potential file.
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2007-06-12 00:19:29 +08:00
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</P>
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2006-09-22 00:22:34 +08:00
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<P>I can be specified in one of two ways. An explicit numeric value can
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2008-03-19 04:18:54 +08:00
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be used, as in the 1st example above. Or a wild-card asterisk can be
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2006-09-22 00:22:34 +08:00
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used to set the mass for multiple atom types. This takes the form "*"
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or "*n" or "n*" or "m*n". If N = the number of atom types, then an
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2008-03-01 09:13:20 +08:00
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asterisk with no numeric values means all types from 1 to N. A leading
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asterisk means all types from 1 to n (inclusive). A trailing asterisk
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means all types from n to N (inclusive). A middle asterisk means all
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2006-09-22 00:22:34 +08:00
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types from m to n (inclusive).
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</P>
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2007-06-12 00:19:29 +08:00
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<P>A line in a data file that specifies mass uses the same format as the
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arguments of the mass command in an input script, except that no
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2008-03-19 04:18:54 +08:00
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wild-card asterisk can be used. For example, under the "Masses"
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2006-09-22 00:22:34 +08:00
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section of a data file, the line that corresponds to the 1st example
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above would be listed as
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</P>
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<PRE>1 1.0
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</PRE>
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<P><B>Restrictions:</B>
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</P>
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<P>This command must come after the simulation box is defined by a
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<A HREF = "read_data.html">read_data</A>, <A HREF = "read_restart.html">read_restart</A>, or
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<A HREF = "create_box.html">create_box</A> command.
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</P>
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<P>All masses must be defined before a simulation is run (if the atom
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style requires masses be set). They must also all be defined before a
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<A HREF = "velocity.html">velocity</A> or <A HREF = "fix_shake.html">fix shake</A> command is
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used.
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</P>
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<P><B>Related commands:</B> none
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</P>
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<P><B>Default:</B> none
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</P>
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</HTML>
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