forked from lijiext/lammps
86 lines
2.2 KiB
HTML
86 lines
2.2 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>angle_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>angle_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>angle_style class2
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angle_coeff * 75.0
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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> angle style uses the potential
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</P>
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<CENTER><IMG SRC = "Eqs/angle_class2.jpg">
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</CENTER>
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<P>where Ea is the angle term, Ebb is a bond-bond term, and Eba is a
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bond-angle term. Theta0 is the equilibrium angle and r1 and r2 are
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the equilibrium bond lengths.
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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>For this style, only coefficients for the Ea formula can be specified
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in the input script. These are the 4 coefficients:
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</P>
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<UL><LI>theta0 (degrees)
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<LI>K2 (energy/radian^2)
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<LI>K3 (energy/radian^2)
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<LI>K4 (energy/radian^2)
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</UL>
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<P>Theta0 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 Ebb and Eba formulas must be specified in the
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data file.
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</P>
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<P>For the Ebb formula, the coefficients are listed under a "BondBond
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Coeffs" heading and each line lists 3 coefficients:
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</P>
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<UL><LI>M (energy/distance^2)
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<LI>r1 (distance)
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<LI>r2 (distance)
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</UL>
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<P>For the Eba formula, the coefficients are listed under a "BondAngle
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Coeffs" heading and each line lists 4 coefficients:
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</P>
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<UL><LI>N1 (energy/distance^2)
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<LI>N2 (energy/distance^2)
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<LI>r1 (distance)
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<LI>r2 (distance)
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</UL>
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<P>The theta0 value in the Eba formula is not specified, since it is the
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same value from the Ea formula.
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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 is part of the "class2" package. It is only enabled
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if LAMMPS was built with that package. See the <A HREF = "Section_start.html#2_2">Making
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LAMMPS</A> section for more info.
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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 = "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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