forked from lijiext/lammps
75 lines
2.8 KiB
HTML
75 lines
2.8 KiB
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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>lattice command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>lattice style value
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</PRE>
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<UL><LI>style = <I>none</I> or <I>sc</I> or <I>bcc</I> or <I>fcc</I> or <I>sq</I> or <I>sq2</I> or <I>hex</I> or <I>diamond</I>
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<PRE> <I>none</I> value = none
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for all other styles:
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value = reduced density (for LJ units)
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value = cubic lattice constant in Angstroms (for real or metal units)
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</PRE>
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>lattice fcc 3.52
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lattice hex 0.85
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lattice none
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Define a lattice type and lattice constant. This is required before
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using a commands that (optionally) use the lattice, such as
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<A HREF = "create_atoms.html">create_atoms</A> or <A HREF = "region.html">region</A>. The lattice
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type must be consistent with the dimension of the simulation - see the
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<A HREF = "dimension.html">dimension</A> command. Styles <I>sc</I> or <I>bcc</I> or <I>fcc</I> or
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<I>diamond</I> are for 3d problems. Styles <I>sq</I> or <I>sq2</I> or <I>hex</I> are for
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2d problems. Lattices of style <I>fcc</I>, <I>bcc</I>, <I>hex</I>, or <I>diamond</I> are
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described in any solid-state physics text. A <I>sc</I> lattice is simple
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cubic, with atoms at the corners of a cube. A <I>sq</I> lattice is square
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with atoms at the corners of a square. A <I>sq2</I> lattice is a <I>sq</I>
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lattice with an additional atom at the center of the square.
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</P>
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<P>For unit style <I>real</I> or <I>metal</I>, the specified value is the cubic
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lattice constant in Angstroms. For unit style <I>lj</I>, the value is the
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reduced density (rho*) which LAMMPS converts into a cubic lattice
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constant. For 3d problems, the relationship "rho* = rho sigma^3" is
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used for the conversion, where rho = N/V with V = the volume of the
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cubic cell and N = 4 for <I>fcc</I>, 2 for <I>bcc</I>, 1 for <I>sc</I>, and 8 for
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<I>diamond</I> lattices. For 2d problems, the relationship "rho* = rho
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sigma^2" is used for the conversion, where N = 2 for <I>sq2</I> or <I>hex</I>
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and 1 for <I>sq</I>. In the hex case, the unit cell is actually
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rectangular; it is extended by a factor of sqrt(3) in the y-dimension.
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</P>
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<P>The command "lattice none" can be used to turn off the lattice
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setting. Any command that attempts to use a lattice constant will
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then generate an error.
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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 = "dimension.html">dimension</A>, <A HREF = "orient.html">orient</A>,
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<A HREF = "origin.html">origin</A>, <A HREF = "create_atoms.html">create_atoms</A>,
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<A HREF = "region.html">region</A>
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</P>
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<P><B>Default:</B>
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</P>
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<PRE>lattice none
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</PRE>
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</HTML>
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