forked from lijiext/lammps
199 lines
5.8 KiB
Plaintext
199 lines
5.8 KiB
Plaintext
.. index:: dihedral_style class2
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dihedral_style class2 command
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=============================
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dihedral_style class2/omp 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 class2
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Examples
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""""""""
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.. parsed-literal::
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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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Description
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"""""""""""
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The *class2* dihedral style uses the potential
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.. image:: Eqs/dihedral_class2.jpg
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:align: center
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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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Theta1 and theta2 are equilibrium angles and r1 r2 r3 are equilibrium
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bond lengths.
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See :ref:`(Sun) <Sun>` for a description of the COMPASS class2 force field.
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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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:doc:`dihedral_coeff <dihedral_coeff>` 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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:doc:`read_data <read_data>` or :doc:`read_restart <read_restart>`
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commands.
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These are the 6 coefficients for the Ed formula:
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* K1 (energy)
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* phi1 (degrees)
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* K2 (energy)
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* phi2 (degrees)
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* K3 (energy)
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* phi3 (degrees)
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For the Embt formula, each line in a
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:doc:`dihedral_coeff <dihedral_coeff>` 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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* mbt
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* A1 (energy/distance)
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* A2 (energy/distance)
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* A3 (energy/distance)
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* r2 (distance)
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For the Eebt formula, each line in a
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:doc:`dihedral_coeff <dihedral_coeff>` 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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* ebt
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* B1 (energy/distance)
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* B2 (energy/distance)
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* B3 (energy/distance)
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* C1 (energy/distance)
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* C2 (energy/distance)
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* C3 (energy/distance)
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* r1 (distance)
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* r3 (distance)
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For the Eat formula, each line in a
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:doc:`dihedral_coeff <dihedral_coeff>` 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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* at
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* D1 (energy/radian)
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* D2 (energy/radian)
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* D3 (energy/radian)
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* E1 (energy/radian)
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* E2 (energy/radian)
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* E3 (energy/radian)
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* theta1 (degrees)
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* theta2 (degrees)
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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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For the Eaat formula, each line in a
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:doc:`dihedral_coeff <dihedral_coeff>` 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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* aat
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* M (energy/radian^2)
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* theta1 (degrees)
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* theta2 (degrees)
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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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For the Ebb13 formula, each line in a
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:doc:`dihedral_coeff <dihedral_coeff>` 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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* bb13
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* N (energy/distance^2)
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* r1 (distance)
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* r3 (distance)
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----------
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Styles with a *cuda*, *gpu*, *intel*, *kk*, *omp*, or *opt* suffix are
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functionally the same as the corresponding style without the suffix.
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They have been optimized to run faster, depending on your available
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hardware, as discussed in :doc:`Section_accelerate <Section_accelerate>`
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of the manual. The accelerated styles take the same arguments and
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should produce the same results, except for round-off and precision
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issues.
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These accelerated styles are part of the USER-CUDA, GPU, USER-INTEL,
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KOKKOS, USER-OMP and OPT packages, respectively. They are only
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enabled if LAMMPS was built with those packages. See the :ref:`Making LAMMPS <start_3>` section for more info.
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You can specify the accelerated styles explicitly in your input script
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by including their suffix, or you can use the :ref:`-suffix command-line switch <start_7>` when you invoke LAMMPS, or you can
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use the :doc:`suffix <suffix>` command in your input script.
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See :doc:`Section_accelerate <Section_accelerate>` of the manual for
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more instructions on how to use the accelerated styles effectively.
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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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CLASS2 package. See the :ref:`Making LAMMPS <start_3>`
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section for more info on packages.
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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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----------
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.. _Sun:
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**(Sun)** Sun, J Phys Chem B 102, 7338-7364 (1998).
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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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