forked from lijiext/lammps
111 lines
3.3 KiB
Plaintext
111 lines
3.3 KiB
Plaintext
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.. index:: dihedral_style hybrid
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dihedral_style hybrid command
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=============================
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Syntax
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""""""
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.. parsed-literal::
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dihedral_style hybrid style1 style2 ...
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* style1,style2 = list of one or more dihedral styles
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Examples
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""""""""
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.. parsed-literal::
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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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Description
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"""""""""""
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The *hybrid* 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 *harmonic* potential and dihedrals in the wall
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boundary (of dihedral type 2) could be computed with a *helix*
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potential. The assignment of dihedral type to style is made via the
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:doc:`dihedral_coeff <dihedral_coeff>` command or in the data file.
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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 *harmonic* 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 *helix*
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potential with coefficients 10, 10, 10 for A, B, C.
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If dihedral coefficients are specified in the data file read via the
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:doc:`read_data <read_data>` 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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.. parsed-literal::
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Dihedral Coeffs
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.. parsed-literal::
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1 harmonic 6.0 1 3
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2 helix 10 10 10
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...
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If *class2* 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. *class2* 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 *class2*, you must use an
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dihedral style of *skip* as a placeholder, e.g.
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.. parsed-literal::
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AngleTorsion Coeffs
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.. parsed-literal::
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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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Note that it is not necessary to use the dihedral style *skip* 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 *class2*.
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A dihedral style of *none* 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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----------
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Restrictions
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""""""""""""
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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 :ref:`Making LAMMPS <start_3>` section for more info on packages.
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Unlike other dihedral styles, the hybrid dihedral style does not store
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dihedral coefficient info for individual sub-styles in a :doc:`binary restart files <restart>`. 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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Related commands
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""""""""""""""""
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:doc:`dihedral_coeff <dihedral_coeff>`
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**Default:** none
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.. _lws: http://lammps.sandia.gov
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.. _ld: Manual.html
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.. _lc: Section_commands.html#comm
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