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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<HR>
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<H3>dihedral_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>dihedral_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>dihedral_style class2
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dihedral_coeff 1 100 75 100 70 80 60
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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> dihedral style uses the potential
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</P>
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<CENTER><IMG SRC = "Eqs/dihedral_class2.jpg">
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</CENTER>
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<P>where Ed is the dihedral term, Embt is a middle-bond-torsion term,
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Eebt is an end-bond-torsion term, Eat is an angle-torsion term, Eaat
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is an angle-angle-torsion term, and Ebb13 is a bond-bond-13 term.
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</P>
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<P>Theta1 and theta2 are equilibrium angles and r1 r2 r3 are equilibrium
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bond lengths.
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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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2007-06-25 22:36:36 +08:00
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<P>For this style, coefficients for the Ed formula can be specified in
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either the input script or data file. These are the 6 coefficients:
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2006-09-22 00:22:34 +08:00
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</P>
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<UL><LI>K1 (energy)
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<LI>phi1 (degrees)
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<LI>K2 (energy)
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<LI>phi2 (degrees)
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<LI>K3 (energy)
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<LI>phi3 (degrees)
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</UL>
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2007-06-25 22:36:36 +08:00
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<P>Coefficients for all the other formulas can only be specified in the
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data file.
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2006-09-22 00:22:34 +08:00
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</P>
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<P>For the Embt formula, the coefficients are listed under a
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"MiddleBondTorsion Coeffs" heading and each line lists 4 coefficients:
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</P>
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<UL><LI>A1 (energy/distance)
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<LI>A2 (energy/distance)
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<LI>A3 (energy/distance)
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<LI>r2 (distance)
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</UL>
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<P>For the Eebt formula, the coefficients are listed under a
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"EndBondTorsion Coeffs" heading and each line lists 8 coefficients:
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</P>
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<UL><LI>B1 (energy/distance)
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<LI>B2 (energy/distance)
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<LI>B3 (energy/distance)
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<LI>C1 (energy/distance)
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<LI>C2 (energy/distance)
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<LI>C3 (energy/distance)
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<LI>r1 (distance)
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<LI>r3 (distance)
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</UL>
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<P>For the Eat formula, the coefficients are listed under a "AngleTorsion
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Coeffs" heading and each line lists 8 coefficients:
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</P>
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<UL><LI>D1 (energy/radian)
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<LI>D2 (energy/radian)
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<LI>D3 (energy/radian)
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<LI>E1 (energy/radian)
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<LI>E2 (energy/radian)
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<LI>E3 (energy/radian)
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<LI>theta1 (degrees)
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<LI>theta2 (degrees)
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</UL>
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<P>Theta1 and theta2 are specified in degrees, but LAMMPS converts them
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to radians internally; hence the units of D and E are in
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energy/radian.
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</P>
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<P>For the Eaat formula, the coefficients are listed under a
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"AngleAngleTorsion Coeffs" heading and each line lists 3 coefficients:
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</P>
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<UL><LI>M (energy/radian^2)
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<LI>theta1 (degrees)
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<LI>theta2 (degrees)
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</UL>
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<P>Theta1 and theta2 are specified in degrees, but LAMMPS converts them
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to radians internally; hence the units of M are in energy/radian^2.
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</P>
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<P>For the Ebb13 formula, the coefficients are listed under a "BondBond13
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Coeffs" heading and each line lists 3 coefficients:
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</P>
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<UL><LI>N (energy/distance^2)
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<LI>r1 (distance)
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<LI>r3 (distance)
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</UL>
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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 dihedral 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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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 = "dihedral_coeff.html">dihedral_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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