forked from lijiext/lammps
185 lines
6.3 KiB
HTML
185 lines
6.3 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>dihedral_style class2 command
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</H3>
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<H3>dihedral_style class2/omp 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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dihedral_coeff * mbt 3.5945 0.1704 -0.5490 1.5228
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dihedral_coeff * ebt 0.3417 0.3264 -0.9036 0.1368 0.0 -0.8080 1.0119 1.1010
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dihedral_coeff 2 at 0.0 -0.1850 -0.7963 -2.0220 0.0 -0.3991 110.2453 105.1270
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dihedral_coeff * aat -13.5271 110.2453 105.1270
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dihedral_coeff * bb13 0.0 1.0119 1.1010
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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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<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>Coefficients for the Ed, Embt, Eebt, Eat, Eaat, and Ebb13 formulas
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must be defined for each dihedral type via the
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<A HREF = "dihedral_coeff.html">dihedral_coeff</A> command as in the example above,
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or in the data file or restart files read by the
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<A HREF = "read_data.html">read_data</A> or <A HREF = "read_restart.html">read_restart</A>
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commands.
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</P>
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<P>These are the 6 coefficients for the Ed formula:
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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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<P>For the Embt formula, each line in a
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<A HREF = "dihedral_coeff.html">dihedral_coeff</A> command in the input script lists
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5 coefficients, the first of which is "mbt" to indicate they are
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MiddleBondTorsion coefficients. In a data file, these coefficients
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should be listed under a "MiddleBondTorsion Coeffs" heading and you
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must leave out the "mbt", i.e. only list 4 coefficients after the
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dihedral type.
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</P>
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<UL><LI>mbt
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<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, each line in a
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<A HREF = "dihedral_coeff.html">dihedral_coeff</A> command in the input script lists
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9 coefficients, the first of which is "ebt" to indicate they are
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EndBondTorsion coefficients. In a data file, these coefficients
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should be listed under a "EndBondTorsion Coeffs" heading and you must
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leave out the "ebt", i.e. only list 8 coefficients after the dihedral
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type.
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</P>
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<UL><LI>ebt
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<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, each line in a
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<A HREF = "dihedral_coeff.html">dihedral_coeff</A> command in the input script lists
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9 coefficients, the first of which is "at" to indicate they are
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AngleTorsion coefficients. In a data file, these coefficients should
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be listed under a "AngleTorsion Coeffs" heading and you must leave out
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the "at", i.e. only list 8 coefficients after the dihedral type.
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</P>
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<UL><LI>at
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<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, each line in a
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<A HREF = "dihedral_coeff.html">dihedral_coeff</A> command in the input script lists
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4 coefficients, the first of which is "aat" to indicate they are
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AngleAngleTorsion coefficients. In a data file, these coefficients
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should be listed under a "AngleAngleTorsion Coeffs" heading and you
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must leave out the "aat", i.e. only list 3 coefficients after the
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dihedral type.
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</P>
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<UL><LI>aat
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<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, each line in a
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<A HREF = "dihedral_coeff.html">dihedral_coeff</A> command in the input script lists
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4 coefficients, the first of which is "bb13" to indicate they are
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BondBond13 coefficients. In a data file, these coefficients should be
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listed under a "BondBond13 Coeffs" heading and you must leave out the
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"bb13", i.e. only list 3 coefficients after the dihedral type.
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</P>
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<UL><LI>bb13
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<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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<HR>
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<P>Styles with a <I>cuda</I>, <I>gpu</I>, <I>omp</I>, or <I>opt</I> suffix are functionally
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the same as the corresponding style without the suffix. They have
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been optimized to run faster, depending on your available hardware, as
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discussed in <A HREF = "Section_accelerate.html">Section_accelerate</A> of the
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manual. The accelerated styles take the same arguments and should
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produce the same results, except for round-off and precision issues.
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</P>
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<P>These accelerated styles are part of the USER-CUDA, GPU, USER-OMP and OPT
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packages, respectively. They are only enabled if LAMMPS was built with
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those packages. See the <A HREF = "Section_start.html#start_3">Making LAMMPS</A>
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section for more info.
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</P>
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<P>You can specify the accelerated styles explicitly in your input script
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by including their suffix, or you can use the <A HREF = "Section_start.html#start_7">-suffix command-line
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switch</A> when you invoke LAMMPS, or you can
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use the <A HREF = "suffix.html">suffix</A> command in your input script.
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</P>
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<P>See <A HREF = "Section_accelerate.html">Section_accelerate</A> of the manual for
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more instructions on how to use the accelerated styles effectively.
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</P>
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<HR>
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<P><B>Restrictions:</B>
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</P>
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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#start_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 = "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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<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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