forked from lijiext/lammps
98 lines
3.5 KiB
HTML
98 lines
3.5 KiB
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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</CENTER>
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<HR>
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<H3>dihedral_style hybrid 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 hybrid style1 style2 ...
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</PRE>
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<UL><LI>style1,style2 = list of one or more dihedral styles
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>dihedral_style hybrid harmonic helix
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dihedral_coeff 1 harmonic 6.0 1 3
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dihedral_coeff 2* helix 10 10 10
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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>hybrid</I> style enables the use of multiple dihedral styles in one
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simulation. An dihedral style is assigned to each dihedral type. For
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example, dihedrals in a polymer flow (of dihedral type 1) could be
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computed with a <I>harmonic</I> potential and dihedrals in the wall
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boundary (of dihedral type 2) could be computed with a <I>helix</I>
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potential. The assignment of dihedral type to style is made via the
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<A HREF = "dihedral_coeff.html">dihedral_coeff</A> command or in the data file.
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</P>
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<P>In the dihedral_coeff commands, the name of a dihedral style must be
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added after the dihedral type, with the remaining coefficients being
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those appropriate to that style. In the example above, the 2
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dihedral_coeff commands set dihedrals of dihedral type 1 to be
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computed with a <I>harmonic</I> potential with coefficients 6.0, 1, 3 for
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K, d, n. All other dihedral types (2-N) are computed with a <I>helix</I>
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potential with coefficients 10, 10, 10 for A, B, C.
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</P>
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<P>If dihedral coefficients are specified in the data file read via the
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<A HREF = "read_data.html">read_data</A> command, then the same rule applies.
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E.g. "harmonic" or "helix", must be added after the dihedral type, for
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each line in the "Dihedral Coeffs" section, e.g.
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</P>
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<PRE>Dihedral Coeffs
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</PRE>
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<PRE>1 harmonic 6.0 1 3
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2 helix 10 10 10
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...
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</PRE>
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<P>If <I>class2</I> is one of the dihedral hybrid styles, the same rule holds
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for specifying additional AngleTorsion (and EndBondTorsion, etc)
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coefficients either via the input script or in the data file.
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I.e. <I>class2</I> must be added to each line after the dihedral type. For
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lines in the AngleTorsion (or EndBondTorsion, etc) section of the data
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file for dihedral types that are not <I>class2</I>, you must use an
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dihedral style of <I>skip</I> as a placeholder, e.g.
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</P>
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<PRE>AngleTorsion Coeffs
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</PRE>
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<PRE>1 skip
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2 class2 1.0 1.0 1.0 3.0 3.0 3.0 30.0 50.0
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...
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</PRE>
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<P>Note that it is not necessary to use the dihedral style <I>skip</I> in the
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input script, since AngleTorsion (or EndBondTorsion, etc) coefficients
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need not be specified at all for dihedral types that are not <I>class2</I>.
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</P>
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<P>A dihedral style of <I>none</I> with no additional coefficients can be used
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in place of a dihedral style, either in a input script dihedral_coeff
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command or in the data file, if you desire to turn off interactions
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for specific dihedral types.
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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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MOLECULE package (which it is by default). See the <A HREF = "Section_start.html#start_3">Making
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LAMMPS</A> section for more info on packages.
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</P>
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<P>Unlike other dihedral styles, the hybrid dihedral style does not store
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dihedral coefficient info for individual sub-styles in a <A HREF = "restart.html">binary
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restart files</A>. Thus when retarting a simulation from a
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restart file, you need to re-specify dihedral_coeff commands.
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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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</HTML>
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