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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>
</CENTER>
<HR>
<H3>angle_style class2 command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>angle_style class2
</PRE>
<P><B>Examples:</B>
</P>
<PRE>angle_style class2
angle_coeff * 75.0
</PRE>
<P><B>Description:</B>
</P>
<P>The <I>class2</I> angle style uses the potential
</P>
<CENTER><IMG SRC = "Eqs/angle_class2.jpg">
</CENTER>
<P>where Ea is the angle term, Ebb is a bond-bond term, and Eba is a
bond-angle term. Theta0 is the equilibrium angle and r1 and r2 are
the equilibrium bond lengths.
</P>
<P>See <A HREF = "#Sun">(Sun)</A> for a description of the COMPASS class2 force field.
</P>
<P>For this style, coefficients for the Ea formula can be specified in
the input script or data file. These are the 4 coefficients:
</P>
<UL><LI>theta0 (degrees)
<LI>K2 (energy/radian^2)
<LI>K3 (energy/radian^3)
<LI>K4 (energy/radian^4)
</UL>
<P>Theta0 is specified in degrees, but LAMMPS converts it to radians
internally; hence the units of the various K are in per-radian.
</P>
<P>Coefficients for the Ebb and Eba formulas can only be specified in the
data file.
</P>
<P>For the Ebb formula, the coefficients are listed under a "BondBond
Coeffs" heading and each line lists 3 coefficients:
</P>
<UL><LI>M (energy/distance^2)
<LI>r1 (distance)
<LI>r2 (distance)
</UL>
<P>For the Eba formula, the coefficients are listed under a "BondAngle
Coeffs" heading and each line lists 4 coefficients:
</P>
<UL><LI>N1 (energy/distance^2)
<LI>N2 (energy/distance^2)
<LI>r1 (distance)
<LI>r2 (distance)
</UL>
<P>The theta0 value in the Eba formula is not specified, since it is the
same value from the Ea formula.
</P>
<P><B>Restrictions:</B>
</P>
<P>This angle style can only be used if LAMMPS was built with the
"class2" package. See the <A HREF = "Section_start.html#2_3">Making LAMMPS</A>
section for more info on packages.
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "angle_coeff.html">angle_coeff</A>
</P>
<P><B>Default:</B> none
</P>
<HR>
<A NAME = "Sun"></A>
<P><B>(Sun)</B> Sun, J Phys Chem B 102, 7338-7364 (1998).
</P>
</HTML>
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