forked from lijiext/lammps
73 lines
2.2 KiB
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73 lines
2.2 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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<HR>
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<H3>compute centro/atom command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>compute ID group-ID centro/atom
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</PRE>
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<UL><LI>ID, group-ID are documented in <A HREF = "compute.html">compute</A> command
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<LI>centro/atom = style name of this compute command
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>compute 1 all centro/atom
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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 computation that calculates the centro-symmetry parameter for
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each atom in a group. In solid-state systems the centro-symmetry
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parameter is a useful measure of the local lattice disorder around an
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atom and can be used to characterize whether the atom is part of a
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perfect lattice, a local defect (e.g. a dislocation or stacking
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fault), or at a surface.
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</P>
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<P>The value of the centro-symmetry parameter will be 0.0 for atoms not
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in the specified compute group.
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</P>
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<P>This parameter is computed using the following formula from
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<A HREF = "#Kelchner">(Kelchner)</A>
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</P>
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<CENTER><IMG SRC = "Eqs/centro_symmetry.jpg">
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</CENTER>
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<P>where the 12 nearest neighbors are found (for fcc lattices) and Ri and
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Ri+6 are the vectors from the central atom to the opposite pair of
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nearest neighbors. Atoms not in the group are included in the 12
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neighbors used in this calculation.
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</P>
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<P>The neighbor list needed to compute this quantity is constructed each
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time the calculation is performed (i.e. each time a snapshot of atoms
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is dumped). Thus it can be inefficient to compute/dump this quantity
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too frequently or to have multiple compute/dump commands, each of a
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<I>centro/atom</I> style.
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</P>
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<P><B>Output info:</B>
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</P>
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<P>This compute calculates a scalar quantity for each atom, which can be
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accessed by any command that uses per-atom computes as input. See
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<A HREF = "Section_howto.html#4_15">this section</A> for an overview of LAMMPS
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output options.
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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> none
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</P>
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<P><B>Default:</B> none
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</P>
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<HR>
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<A NAME = "Kelchner"></A>
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<P><B>(Kelchner)</B> Kelchner, Plimpton, Hamilton, Phys Rev B, 58, 11085 (1998).
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</P>
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</HTML>
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