forked from lijiext/lammps
69 lines
2.1 KiB
HTML
69 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>improper_style cvff command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>improper_style cvff
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</PRE>
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<P><B>Examples:</B>
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</P>
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<PRE>improper_style cvff
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improper_coeff 1 80.0 -1 4
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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>cvff</I> improper style uses the potential
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</P>
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<CENTER><IMG SRC = "Eqs/improper_cvff.jpg">
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</CENTER>
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<P>where phi is the Wilson out-of-plane angle.
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</P>
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<P>If the 4 atoms in an improper quadruplet (listed in the data file read
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by the <A HREF = "read_data.html">read_data</A> command) are ordered I,J,K,L then
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the Wilson angle is between the plane of I,J,K and the plane of J,K,L.
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This is essentially a dihedral angle, which is why the formula for
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this improper style is the same as for <A HREF = "dihedral_harmonic.html">dihedral_style
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harmonic</A>. Alternatively, you can think of
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atoms J,K,L as being in a plane, and atom I above the plane, and the
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Wilson angle as a measure of how far out-of-plane I is with respect to
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the other 3 atoms.
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</P>
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<P>Note that defining 4 atoms to interact in this way, does not mean that
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bonds necessarily exist between I-J, J-K, or K-L, as they would in a
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linear dihedral. Normally, the bonds I-J, I-K, I-L would exist for an
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improper to be defined between the 4 atoms.
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</P>
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<P>The following coefficients must be defined for each improper type via
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the <A HREF = "improper_coeff.html">improper_coeff</A> command as in the example
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above, or in the data file or restart files read by the
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<A HREF = "read_data.html">read_data</A> or <A HREF = "read_restart.html">read_restart</A>
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commands:
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</P>
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<UL><LI>K (energy)
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<LI>d (+1 or -1)
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<LI>n (0,1,2,3,4,6)
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</UL>
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<P><B>Restrictions:</B>
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</P>
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<P>This improper 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><B>Related commands:</B>
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</P>
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<P><A HREF = "improper_coeff.html">improper_coeff</A>
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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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