2010-10-26 04:29:36 +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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<HR>
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<H3>angle_style cosine/periodic 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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2011-08-26 01:01:01 +08:00
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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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2010-10-26 04:29:36 +08:00
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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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<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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2011-08-26 00:46:23 +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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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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