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_coeff 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_coeff N args
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</PRE>
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2006-09-29 04:27:30 +08:00
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<UL><LI>N = dihedral type (see asterisk form below)
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<LI>args = coefficients for one or more dihedral types
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>dihedral_coeff 1 80.0 1 3
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dihedral_coeff * 80.0 1 3 0.5
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dihedral_coeff 2* 80.0 1 3 0.5
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</PRE>
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<P><B>Description:</B>
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</P>
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<HR>
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<P>Specify the dihedral force field coefficients for one or more dihedral types.
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The number and meaning of the coefficients depends on the dihedral style.
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Dihedral coefficients can also be set in the data file read by the
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<A HREF = "read_data.html">read_data</A> command or in a restart file.
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</P>
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<P>N can be specified in one of two ways. An explicit numeric value can
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be used, as in the 1st example above. Or a wild-card asterisk can be
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used to set the coefficients for multiple dihedral types. This takes the
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form "*" or "*n" or "n*" or "m*n". If N = the number of dihedral types,
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then an asterisk with no numeric values means all types from 1 to N. A
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leading asterisk means all types from 1 to n (inclusive). A trailing
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asterisk means all types from n to N (inclusive). A middle asterisk
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means all types from m to n (inclusive).
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</P>
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<P>Note that using a dihedral_coeff command can override a previous setting
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for the same dihedral type. For example, these commands set the coeffs
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for all dihedral types, then overwrite the coeffs for just dihedral type 2:
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</P>
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<PRE>dihedral_coeff * 80.0 1 3
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dihedral_coeff 2 200.0 1 3
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</PRE>
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<P>A line in a data file that specifies dihedral coefficients uses the exact
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same format as the arguments of the dihedral_coeff command in an input
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script, except that wild-card asterisks should not be used since
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coefficients for all N types must be listed in the file. For example,
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under the "Dihedral Coeffs" section of a data file, the line that
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corresponds to the 1st example above would be listed as
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</P>
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<PRE>1 80.0 1 3
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</PRE>
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2010-11-18 02:25:09 +08:00
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<P>The <A HREF = "dihedral_class2.html">dihedral_style class2</A> is an exception to
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this rule, in that an additional argument is used in the input script
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to allow specification of the cross-term coefficients. See its doc
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page for details.
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</P>
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<HR>
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<P>Here is an alphabetic list of dihedral styles defined in LAMMPS. Click on
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the style to display the formula it computes and coefficients
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specified by the associated <A HREF = "dihedral_coeff.html">dihedral_coeff</A> command:
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</P>
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2007-02-10 05:37:30 +08:00
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<UL><LI><A HREF = "dihedral_none.html">dihedral_style none</A> - turn off dihedral interactions
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<LI><A HREF = "dihedral_hybrid.html">dihedral_style hybrid</A> - define multiple styles of dihedral interactions
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</UL>
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<UL><LI><A HREF = "dihedral_charmm.html">dihedral_style charmm</A> - CHARMM dihedral
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<LI><A HREF = "dihedral_class2.html">dihedral_style class2</A> - COMPASS (class 2) dihedral
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<LI><A HREF = "dihedral_harmonic.html">dihedral_style harmonic</A> - harmonic dihedral
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<LI><A HREF = "dihedral_helix.html">dihedral_style helix</A> - helix dihedral
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<LI><A HREF = "dihedral_multi_harmonic.html">dihedral_style multi/harmonic</A> - multi-harmonic dihedral
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<LI><A HREF = "dihedral_opls.html">dihedral_style opls</A> - OPLS dihedral
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</UL>
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<P>There are also additional dihedral styles submitted by users which are
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included in the LAMMPS distribution. The list of these with links to
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the individual styles are given in the dihedral section of <A HREF = "Section_commands.html#3_5">this
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page</A>.
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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 command must come after the simulation box is defined by a
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<A HREF = "read_data.html">read_data</A>, <A HREF = "read_restart.html">read_restart</A>, or
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<A HREF = "create_box.html">create_box</A> command.
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</P>
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<P>A dihedral style must be defined before any dihedral coefficients are
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set, either in the input script or in a data file.
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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_style.html">dihedral_style</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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