2012-05-23 00:09:28 +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 cossq command
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</H3>
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2012-05-29 22:47:52 +08:00
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<H3>improper_style cossq/omp command
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</H3>
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2012-05-23 00:09:28 +08:00
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<P><B>Syntax:</B>
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</P>
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<PRE>improper_style cossq
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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 cossq
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improper_coeff 1 4.0 0.0
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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>cossq</I> improper style uses the potential
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</P>
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<CENTER><IMG SRC = "Eqs/improper_cossq.jpg">
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</CENTER>
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<P>where x is the improper angle, x0 is its equilibrium value, and K is a
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prefactor.
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</P>
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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 X
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is the angle between the plane of I,J,K and the plane of J,K,L.
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Alternatively, you can think of atoms J,K,L as being in a plane, and
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atom I above the plane, and X as a measure of how far out-of-plane I
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is with respect to the other 3 atoms.
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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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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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</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/radian^2)
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<LI>X0 (degrees)
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</UL>
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<P>X0 is specified in degrees, but LAMMPS converts it to radians
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internally; hence the units of K are in energy/radian^2.
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</P>
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<HR>
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2012-05-29 22:47:52 +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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</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_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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2012-05-23 00:09:28 +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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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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</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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