2006-09-22 00:22:34 +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 class2 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 class2/omp command
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</H3>
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2006-09-22 00:22:34 +08:00
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<P><B>Syntax:</B>
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</P>
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<PRE>improper_style class2
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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 class2
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2010-11-19 01:28:36 +08:00
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improper_coeff 1 100.0 0
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improper_coeff * aa 0.0 0.0 0.0 115.06 130.01 115.06
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2006-09-22 00:22:34 +08:00
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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>class2</I> improper style uses the potential
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</P>
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<CENTER><IMG SRC = "Eqs/improper_class2.jpg">
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</CENTER>
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2007-06-28 23:07:55 +08:00
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<P>where Ei is the improper term and Eaa is an angle-angle term. The 3 X
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2007-06-29 00:06:08 +08:00
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terms in Ei are an average over 3 out-of-plane angles.
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2007-06-28 23:07:55 +08:00
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</P>
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<P>The 4 atoms in an improper quadruplet (listed in the data file read by
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the <A HREF = "read_data.html">read_data</A> command) are ordered I,J,K,L. X_IJKL
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refers to the angle between the plane of I,J,K and the plane of J,K,L,
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and the bond JK lies in both planes. Similarly for X_KJLI and X_LJIK.
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Note that atom J appears in the common bonds (JI, JK, JL) of all 3 X
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terms. Thus J (the 2nd atom in the quadruplet) is the atom of
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2007-06-28 23:25:31 +08:00
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symmetry in the 3 X angles.
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2007-06-28 23:07:55 +08:00
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</P>
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<P>The subscripts on the various theta's refer to different combinations
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of 3 atoms (I,J,K,L) used to form a particular angle. E.g. Theta_IJL
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is the angle formed by atoms I,J,L with J in the middle. Theta1,
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2007-06-28 23:25:31 +08:00
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theta2, theta3 are the equilibrium positions of those angles. Again,
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atom J (the 2nd atom in the quadruplet) is the atom of symmetry in the
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theta angles, since it is always the center atom.
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</P>
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2007-06-29 05:59:10 +08:00
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<P>Since atom J is the atom of symmetry, normally the bonds J-I, J-K, J-L
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would exist for an improper to be defined between the 4 atoms, but
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this is not required.
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2006-09-22 00:22:34 +08:00
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</P>
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2006-09-28 03:12:31 +08:00
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<P>See <A HREF = "#Sun">(Sun)</A> for a description of the COMPASS class2 force field.
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</P>
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2010-11-18 02:20:48 +08:00
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<P>Coefficients for the Ei and Eaa formulas must be defined for each
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improper type via the <A HREF = "improper_coeff.html">improper_coeff</A> command as
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in the example 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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2006-09-22 00:22:34 +08:00
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</P>
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2010-11-18 02:20:48 +08:00
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<P>These are the 2 coefficients for the Ei formula:
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2006-09-22 00:22:34 +08:00
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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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2010-11-18 02:20:48 +08:00
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<P>For the Eaa formula, each line in a
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<A HREF = "improper_coeff.html">improper_coeff</A> command in the input script lists
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7 coefficients, the first of which is "aa" to indicate they are
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AngleAngle coefficients. In a data file, these coefficients should be
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listed under a "AngleAngle Coeffs" heading and you must leave out the
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"aa", i.e. only list 6 coefficients after the improper type.
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2006-09-22 00:22:34 +08:00
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</P>
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2010-11-18 02:20:48 +08:00
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<UL><LI>aa
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<LI>M1 (energy/distance)
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2006-09-22 00:22:34 +08:00
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<LI>M2 (energy/distance)
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<LI>M3 (energy/distance)
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<LI>theta1 (degrees)
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<LI>theta2 (degrees)
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<LI>theta3 (degrees)
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</UL>
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<P>The theta values are specified in degrees, but LAMMPS converts them to
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radians internally; hence the units of M are in energy/radian^2.
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</P>
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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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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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2011-12-01 23:35:32 +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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2011-12-01 23:35:32 +08:00
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</P>
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<HR>
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2006-09-22 00:22:34 +08:00
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<P><B>Restrictions:</B>
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</P>
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2007-06-25 22:36:36 +08:00
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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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CLASS2 package. See the <A HREF = "Section_start.html#start_3">Making LAMMPS</A>
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2007-06-25 22:36:36 +08:00
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section for more info on packages.
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2006-09-22 00:22:34 +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 = "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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2006-09-28 03:12:31 +08:00
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<HR>
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<A NAME = "Sun"></A>
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<P><B>(Sun)</B> Sun, J Phys Chem B 102, 7338-7364 (1998).
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</P>
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2006-09-22 00:22:34 +08:00
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</HTML>
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