2006-09-22 00:22:34 +08:00
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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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<H3>improper_style cvff command
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</H3>
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2011-12-01 23:35:32 +08:00
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<H3>improper_style cvff/omp command
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</H3>
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2006-09-22 00:22:34 +08:00
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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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2012-03-06 00:00:47 +08:00
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<P>where phi is the improper dihedral angle.
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2006-09-22 00:22:34 +08:00
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</P>
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2007-06-28 23:07:55 +08:00
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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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2012-03-06 00:00:47 +08:00
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the improper dihedral angle is between the plane of I,J,K and the
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plane of J,K,L. Note that because this is effectively a dihedral
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angle, the formula for this improper style is the same as for
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<A HREF = "dihedral_harmonic.html">dihedral_style harmonic</A>.
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2007-06-28 23:07:55 +08:00
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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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2007-06-29 05:59:10 +08:00
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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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2007-06-28 23:07:55 +08:00
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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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2006-09-22 00:22:34 +08:00
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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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2011-12-01 23:35:32 +08:00
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<HR>
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2011-12-14 04:35:35 +08:00
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<P>Styles with a <I>cuda</I>, <I>gpu</I>, <I>omp</I>, or <I>opt</I> suffix are functionally
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the same as the corresponding style without the suffix. They have
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been optimized to run faster, depending on your available hardware, as
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discussed in <A HREF = "Section_accelerate.html">Section_accelerate</A> of the
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manual. The accelerated styles take the same arguments and should
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produce the same results, except for round-off and precision issues.
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2011-12-01 23:35:32 +08:00
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</P>
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<P>These accelerated styles are part of the USER-CUDA, GPU, USER-OMP and OPT
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packages, respectively. They are only enabled if LAMMPS was built with
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those packages. See the <A HREF = "Section_start.html#start_3">Making LAMMPS</A>
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section for more info.
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</P>
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<P>You can specify the accelerated styles explicitly in your input script
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2012-01-28 07:39:14 +08:00
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by including their suffix, or you can use the <A HREF = "Section_start.html#start_7">-suffix command-line
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2011-12-01 23:35:32 +08:00
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switch</A> when you invoke LAMMPS, or you can
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use the <A HREF = "suffix.html">suffix</A> command in your input script.
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</P>
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2011-12-14 04:35:35 +08:00
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<P>See <A HREF = "Section_accelerate.html">Section_accelerate</A> of the manual for
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more instructions on how to use the accelerated styles effectively.
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2011-12-01 23:35:32 +08:00
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</P>
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<HR>
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2007-06-25 22:36:36 +08:00
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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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2011-08-27 02:53:00 +08:00
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MOLECULAR package (which it is by default). See the <A HREF = "Section_start.html#start_3">Making
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2007-06-25 22:36:36 +08:00
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LAMMPS</A> section for more info on packages.
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2006-09-22 00:22:34 +08:00
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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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