forked from lijiext/lammps
98 lines
3.3 KiB
HTML
98 lines
3.3 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>angle_style cosine/periodic command
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</H3>
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<H3>angle_style cosine/periodic/omp command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>angle_style cosine/periodic
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</PRE>
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<P><B>Examples:</B>
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</P>
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<PRE>angle_style cosine/periodic
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angle_coeff * 75.0 1 6
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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/periodic</I> angle style uses the following potential, which
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is commonly used in the <A HREF = "Section_howto.html#howto_4">DREIDING</A> force
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field, particularly for organometallic systems where <I>n</I> = 4 might be
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used for an octahedral complex and <I>n</I> = 3 might be used for a
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trigonal center:
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</P>
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<CENTER><IMG SRC = "Eqs/angle_cosine_periodic.jpg">
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</CENTER>
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<P>where C, B and n are coefficients defined for each angle type.
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</P>
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<P>See <A HREF = "#Mayo">(Mayo)</A> for a description of the DREIDING force field
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</P>
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<P>The following coefficients must be defined for each angle type via the
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<A HREF = "angle_coeff.html">angle_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>C (energy)
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<LI>B = 1 or -1
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<LI>n = 1, 2, 3, 4, 5 or 6 for periodicity
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</UL>
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<P>Note that the prefactor C is specified and not the overall force
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constant K = C / n^2. When B = 1, it leads to a minimum for the
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linear geometry. When B = -1, it leads to a maximum for the linear
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geometry.
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</P>
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<HR>
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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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</P>
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<P>You can specify the accelerated styles explicitly in your input script
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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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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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<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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</P>
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<HR>
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<P><B>Restrictions:</B>
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</P>
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<P>This angle 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#start_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 = "angle_coeff.html">angle_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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<HR>
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<A NAME = "Mayo"></A>
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<P><B>(Mayo)</B> Mayo, Olfason, Goddard III, J Phys Chem, 94, 8897-8909
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(1990).
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</P>
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</HTML>
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