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

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