2010-10-26 04:29:32 +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 umbrella 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 umbrella/omp command
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</H3>
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2010-10-26 04:29:32 +08:00
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<P><B>Syntax:</B>
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</P>
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<PRE>improper_style umbrella
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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 umbrella
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improper_coeff 1 100.0 180.0
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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>umbrella</I> improper style uses the following potential, which is
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commonly referred to as a classic inversion and used in the
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2011-08-26 01:01:01 +08:00
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<A HREF = "Section_howto.html#howto_4">DREIDING</A> force field:
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2010-10-26 04:29:32 +08:00
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</P>
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<CENTER><IMG SRC = "Eqs/improper_umbrella.jpg">
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</CENTER>
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<P>where K is the force constant and omega is the angle between the IL
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axis and the IJK plane:
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</P>
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<CENTER><IMG SRC = "Eqs/umbrella.jpg">
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</CENTER>
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<P>If omega0 = 0 the potential term has a minimum for the planar
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structure. Otherwise it has two minima at +/- omega0, with a barrier
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in between.
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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 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>omega0 (degrees)
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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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by including their suffix, or you can use the <A HREF = "Section_start.html#start_6">-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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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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2010-10-26 04:29:32 +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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2010-10-26 04:29:32 +08:00
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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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<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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