2011-08-09 06:50:30 +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>dihedral_style cosine/shift/exp command
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</H3>
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2011-10-07 01:32:51 +08:00
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<H3>dihedral_style cosine/shift/exp/omp command
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</H3>
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2011-08-09 06:50:30 +08:00
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<P><B>Syntax:</B>
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</P>
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<PRE>dihedral_style cosine/shift/exp
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</PRE>
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<P><B>Examples:</B>
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</P>
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<PRE>dihedral_style cosine/shift/exp
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dihedral_coeff 1 10.0 45.0 2.0
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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>cosine/shift/exp</I> dihedral style uses the potential
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</P>
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<CENTER><IMG SRC = "Eqs/dihedral_cosine_shift_exp.jpg">
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</CENTER>
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<P>where Umin, theta, and a are defined for each dihedral type.
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</P>
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<P>The potential is bounded between [-Umin:0] and the minimum is located
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at the angle theta0. The a parameter can be both positive or negative
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and is used to control the spring constant at the equilibrium.
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</P>
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<P>The spring constant is given by k=a exp(a) Umin/ [2 (Exp(a)-1)].
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For a>3 k/Umin = a/2 to better than 5% relative error. For negative
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values of the a parameter, the spring constant is essentially zero,
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and anharmonic terms takes over. The potential is furthermore well
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behaved in the limit a->0, where it has been implemented to linear
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order in a for a < 0.001.
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</P>
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<P>The following coefficients must be defined for each dihedral type via
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the <A HREF = "dihedral_coeff.html">dihedral_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>umin (energy)
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<LI>theta (angle)
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<LI>A (real number)
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</UL>
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2011-10-07 01:32:51 +08:00
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<HR>
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2014-08-15 00:30:25 +08:00
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<P>Styles with a <I>cuda</I>, <I>gpu</I>, <I>intel</I>, <I>kk</I>, <I>omp</I>, or <I>opt</I> suffix are
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functionally the same as the corresponding style without the suffix.
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They have been optimized to run faster, depending on your available
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hardware, as discussed in <A HREF = "Section_accelerate.html">Section_accelerate</A>
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of the manual. The accelerated styles take the same arguments and
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should produce the same results, except for round-off and precision
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issues.
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</P>
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<P>These accelerated styles are part of the USER-CUDA, GPU, USER-INTEL,
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KOKKOS, USER-OMP and OPT packages, respectively. They are only
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enabled if LAMMPS was built with those packages. See the <A HREF = "Section_start.html#start_3">Making
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LAMMPS</A> section for more info.
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2011-10-07 01:32:51 +08:00
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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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2011-10-07 01:32:51 +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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2011-10-07 01:32:51 +08:00
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</P>
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<HR>
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2011-08-09 06:50:30 +08:00
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<P><B>Restrictions:</B>
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</P>
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<P>This dihedral 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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USER-MISC package. See the <A HREF = "Section_start.html#start_3">Making LAMMPS</A>
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section for more info on packages.
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2011-08-09 06:50:30 +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 = "dihedral_coeff.html">dihedral_coeff</A>,
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<A HREF = "angle_cosineshiftexp.html">angle_cosineshiftexp</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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