forked from lijiext/lammps
83 lines
2.8 KiB
HTML
83 lines
2.8 KiB
HTML
<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>
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</CENTER>
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<HR>
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<H3>shape command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>shape I x y z
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</PRE>
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<UL><LI>I = atom type (see asterisk form below)
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<LI>x = x diameter
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<LI>y = y diameter
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<LI>z = z diameter
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>shape 1 1.0 1.0 1.0
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shape * 3.0 1.0 1.0
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shape 2* 3.0 1.0 1.0
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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 shape for all atoms of one or more atom types. Shape values
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can 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 distance units to use.
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</P>
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<P>Currently, only <A HREF = "atom_style.html">atom_style dipole</A> and <A HREF = "atom_style.html">atom_style
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ellipsoid</A> require that shapes be set.
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</P>
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<P>Dipoles use the atom shape to compute a moment of inertia for
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rotational energy. Only the 1st component of the shape is used since
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the particles are assumed to be spherical. The value of the first
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component should be the same as the Lennard-Jones sigma value defined
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in the dipole pair potential, i.e. in <A HREF = "pair_dipole.html">pair_style
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dipole</A>.
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</P>
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<P>Ellipsoids use the atom shape to compute a generalized inertia tensor.
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For example, a shape setting of 3.0 1.0 1.0 defines a particle 3x
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longer in x than in y or z and with a circular cross-section in yz.
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Ellipsoids that are spherical can be defined by setting all 3 shape
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components the same.
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</P>
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<P>The I index can be specified in one of two ways. An explicit numeric
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value can be used, as in the 1st example above. Or a wild-card
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asterisk can be used to set the shape for multiple atom types. This
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takes the form "*" or "*n" or "n*" or "m*n". If N = the number of
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atom types, then an asterisk with no numeric values means all types
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from 1 to N. A leading asterisk means all types from 1 to n
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(inclusive). A trailing asterisk means all types from n to N
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(inclusive). A middle asterisk means all types from m to n
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(inclusive).
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</P>
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<P>A line in a data file that specifies shape uses the same format as the
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arguments of the shape command in an input script, except that no
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wild-card asterisk can be used. For example, under the "Shapes"
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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 1.0 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 shapes must be defined before a simulation is run (if the atom
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style requires shapes be set).
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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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