forked from lijiext/lammps
73 lines
2.1 KiB
HTML
73 lines
2.1 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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<HR>
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<H3>bond_style fene/expand command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>bond_style fene/expand
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</PRE>
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<P><B>Examples:</B>
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</P>
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<PRE>bond_style fene/expand
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bond_coeff 1 30.0 1.5 1.0 1.0 0.5
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>The <I>fene/expand</I> bond style uses the potential
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</P>
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<CENTER><IMG SRC = "Eqs/bond_fene_expand.jpg">
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</CENTER>
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<P>to define a finite extensible nonlinear elastic (FENE) potential
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<A HREF = "#Kremer">(Kremer)</A>, used for bead-spring polymer models. The first
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term is attractive, the 2nd Lennard-Jones term is repulsive.
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</P>
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<P>The <I>fene/expand</I> bond style is similar to <I>fene</I> except that an extra
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shift factor of delta (positive or negative) is added to <I>r</I> to
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effectively change the bead size of the bonded atoms. The first term
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now extends to R0 + delta and the 2nd term is cutoff at 2^(1/6) sigma
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+ delta.
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</P>
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<P>The following coefficients must be defined for each bond type via the
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<A HREF = "bond_coeff.html">bond_coeff</A> command as in the example above, or in
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the data file or restart files read by the <A HREF = "read_data.html">read_data</A>
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or <A HREF = "read_restart.html">read_restart</A> commands:
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</P>
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<UL><LI>K (energy/distance^2)
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<LI>R0 (distance)
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<LI>epsilon (energy)
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<LI>sigma (distance)
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<LI>delta (distance)
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</UL>
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<P><B>Restrictions:</B>
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</P>
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<P>This bond style can only be used if LAMMPS was built with the
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"molecular" package (which it is by default). See the <A HREF = "Section_start.html#2_3">Making
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LAMMPS</A> section for more info on packages.
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</P>
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<P>You typically should specify <A HREF = "special_bonds.html">special_bonds 0 1 1</A>
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to use this bond style. LAMMPS will issue a warning it that's not the
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case.
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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 = "bond_coeff.html">bond_coeff</A>, <A HREF = "delete_bonds.html">delete_bonds</A>
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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 = "Kremer"></A>
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<P><B>(Kremer)</B> Kremer, Grest, J Chem Phys, 92, 5057 (1990).
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</P>
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</HTML>
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