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rLAMMPS lammps
dihedral_style_class2.html
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<HTML>
<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>dihedral_style class2 command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>dihedral_style class2
</PRE>
<P><B>Examples:</B>
</P>
<PRE>dihedral_style class2
dihedral_coeff 1 100 75 100 70 80 60
</PRE>
<P><B>Description:</B>
</P>
<P>The <I>class2</I> dihedral style uses the potential
</P>
<CENTER><IMG SRC = "Eqs/dihedral_class2.jpg">
</CENTER>
<P>where Ed is the dihedral term, Embt is a middle-bond-torsion term,
Eebt is an end-bond-torsion term, Eat is an angle-torsion term, Eaat
is an angle-angle-torsion term, and Ebb13 is a bond-bond-13 term.
</P>
<P>Theta1 and theta2 are equilibrium angles and r1 r2 r3 are equilibrium
bond lengths.
</P>
<P>For this style, only coefficients for the Ed formula can be specified
in the input script. These are the 6 coefficients:
</P>
<UL><LI>K1 (energy)
<LI>phi1 (degrees)
<LI>K2 (energy)
<LI>phi2 (degrees)
<LI>K3 (energy)
<LI>phi3 (degrees)
</UL>
<P>Coefficients for all the other formulas must be specified in the data
file.
</P>
<P>For the Embt formula, the coefficients are listed under a
"MiddleBondTorsion Coeffs" heading and each line lists 4 coefficients:
</P>
<UL><LI>A1 (energy/distance)
<LI>A2 (energy/distance)
<LI>A3 (energy/distance)
<LI>r2 (distance)
</UL>
<P>For the Eebt formula, the coefficients are listed under a
"EndBondTorsion Coeffs" heading and each line lists 8 coefficients:
</P>
<UL><LI>B1 (energy/distance)
<LI>B2 (energy/distance)
<LI>B3 (energy/distance)
<LI>C1 (energy/distance)
<LI>C2 (energy/distance)
<LI>C3 (energy/distance)
<LI>r1 (distance)
<LI>r3 (distance)
</UL>
<P>For the Eat formula, the coefficients are listed under a "AngleTorsion
Coeffs" heading and each line lists 8 coefficients:
</P>
<UL><LI>D1 (energy/radian)
<LI>D2 (energy/radian)
<LI>D3 (energy/radian)
<LI>E1 (energy/radian)
<LI>E2 (energy/radian)
<LI>E3 (energy/radian)
<LI>theta1 (degrees)
<LI>theta2 (degrees)
</UL>
<P>Theta1 and theta2 are specified in degrees, but LAMMPS converts them
to radians internally; hence the units of D and E are in
energy/radian.
</P>
<P>For the Eaat formula, the coefficients are listed under a
"AngleAngleTorsion Coeffs" heading and each line lists 3 coefficients:
</P>
<UL><LI>M (energy/radian^2)
<LI>theta1 (degrees)
<LI>theta2 (degrees)
</UL>
<P>Theta1 and theta2 are specified in degrees, but LAMMPS converts them
to radians internally; hence the units of M are in energy/radian^2.
</P>
<P>For the Ebb13 formula, the coefficients are listed under a "BondBond13
Coeffs" heading and each line lists 3 coefficients:
</P>
<UL><LI>N (energy/distance^2)
<LI>r1 (distance)
<LI>r3 (distance)
</UL>
<P><B>Restrictions:</B>
</P>
<P>Dihedral styles can only be set for atom styles that allow dihedrals to be
defined.
</P>
<P>This dihedral style is part of the "class2" package. It is only
enabled if LAMMPS was built with that package. See the <A HREF = "Section_start.html#2_2">Making
LAMMPS</A> section for more info.
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "dihedral_coeff.html">dihedral_coeff</A>
</P>
<P><B>Default:</B> none
</P>
</HTML>
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