forked from lijiext/lammps
84 lines
2.5 KiB
HTML
84 lines
2.5 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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<H3>improper_style class2 command
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</H3>
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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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improper_coeff 1 100.0 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>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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<P>where Ei is the improper term and Eaa is an angle-angle term. The chi
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used in Ei is an average over 3 possible chi orientations. The
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subscripts on the various theta's refer to different combinations of
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atoms i,j,k,l used to form the angle; theta1, theta2, theta3 are the
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equilibrium positions of those angles.
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</P>
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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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<P>The following coefficients must be defined for each improper type via the
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<A HREF = "improper_coeff.html">improper_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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<P>For this style, coefficients for the Ei formula can be specified in
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eiher the input script or data file. These are the 2 coefficients:
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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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<P>Coefficients for the Eaa formula can only be specified in the data
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file. For the Eaa formula, the coefficients are listed under a
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"AngleAngle Coeffs" heading and each line lists 6 coefficients:
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</P>
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<UL><LI>M1 (energy/distance)
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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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<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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"class2" package. See the <A HREF = "Section_start.html#2_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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<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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</HTML>
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