.. index:: dihedral_style class2 dihedral_style class2 command ============================= dihedral_style class2/omp command ================================= Syntax """""" .. parsed-literal:: dihedral_style class2 Examples """""""" .. parsed-literal:: dihedral_style class2 dihedral_coeff 1 100 75 100 70 80 60 dihedral_coeff * mbt 3.5945 0.1704 -0.5490 1.5228 dihedral_coeff * ebt 0.3417 0.3264 -0.9036 0.1368 0.0 -0.8080 1.0119 1.1010 dihedral_coeff 2 at 0.0 -0.1850 -0.7963 -2.0220 0.0 -0.3991 110.2453 105.1270 dihedral_coeff * aat -13.5271 110.2453 105.1270 dihedral_coeff * bb13 0.0 1.0119 1.1010 Description """"""""""" The *class2* dihedral style uses the potential .. image:: Eqs/dihedral_class2.jpg :align: center where Ed is the dihedral term, Embt is a middle-bond-torsion term, Eebt is an end-bond-torsion term, Eat is an angle-torsion term, Eaat is an angle-angle-torsion term, and Ebb13 is a bond-bond-13 term. Theta1 and theta2 are equilibrium angles and r1 r2 r3 are equilibrium bond lengths. See :ref:`(Sun) ` for a description of the COMPASS class2 force field. Coefficients for the Ed, Embt, Eebt, Eat, Eaat, and Ebb13 formulas must be defined for each dihedral type via the :doc:`dihedral_coeff ` command as in the example above, or in the data file or restart files read by the :doc:`read_data ` or :doc:`read_restart ` commands. These are the 6 coefficients for the Ed formula: * K1 (energy) * phi1 (degrees) * K2 (energy) * phi2 (degrees) * K3 (energy) * phi3 (degrees) For the Embt formula, each line in a :doc:`dihedral_coeff ` command in the input script lists 5 coefficients, the first of which is "mbt" to indicate they are MiddleBondTorsion coefficients. In a data file, these coefficients should be listed under a "MiddleBondTorsion Coeffs" heading and you must leave out the "mbt", i.e. only list 4 coefficients after the dihedral type. * mbt * A1 (energy/distance) * A2 (energy/distance) * A3 (energy/distance) * r2 (distance) For the Eebt formula, each line in a :doc:`dihedral_coeff ` command in the input script lists 9 coefficients, the first of which is "ebt" to indicate they are EndBondTorsion coefficients. In a data file, these coefficients should be listed under a "EndBondTorsion Coeffs" heading and you must leave out the "ebt", i.e. only list 8 coefficients after the dihedral type. * ebt * B1 (energy/distance) * B2 (energy/distance) * B3 (energy/distance) * C1 (energy/distance) * C2 (energy/distance) * C3 (energy/distance) * r1 (distance) * r3 (distance) For the Eat formula, each line in a :doc:`dihedral_coeff ` command in the input script lists 9 coefficients, the first of which is "at" to indicate they are AngleTorsion coefficients. In a data file, these coefficients should be listed under a "AngleTorsion Coeffs" heading and you must leave out the "at", i.e. only list 8 coefficients after the dihedral type. * at * D1 (energy/radian) * D2 (energy/radian) * D3 (energy/radian) * E1 (energy/radian) * E2 (energy/radian) * E3 (energy/radian) * theta1 (degrees) * theta2 (degrees) Theta1 and theta2 are specified in degrees, but LAMMPS converts them to radians internally; hence the units of D and E are in energy/radian. For the Eaat formula, each line in a :doc:`dihedral_coeff ` command in the input script lists 4 coefficients, the first of which is "aat" to indicate they are AngleAngleTorsion coefficients. In a data file, these coefficients should be listed under a "AngleAngleTorsion Coeffs" heading and you must leave out the "aat", i.e. only list 3 coefficients after the dihedral type. * aat * M (energy/radian^2) * theta1 (degrees) * theta2 (degrees) Theta1 and theta2 are specified in degrees, but LAMMPS converts them to radians internally; hence the units of M are in energy/radian^2. For the Ebb13 formula, each line in a :doc:`dihedral_coeff ` command in the input script lists 4 coefficients, the first of which is "bb13" to indicate they are BondBond13 coefficients. In a data file, these coefficients should be listed under a "BondBond13 Coeffs" heading and you must leave out the "bb13", i.e. only list 3 coefficients after the dihedral type. * bb13 * N (energy/distance^2) * r1 (distance) * r3 (distance) ---------- Styles with a *cuda*\ , *gpu*\ , *intel*\ , *kk*\ , *omp*\ , or *opt* suffix are functionally the same as the corresponding style without the suffix. They have been optimized to run faster, depending on your available hardware, as discussed in :doc:`Section_accelerate ` of the manual. The accelerated styles take the same arguments and should produce the same results, except for round-off and precision issues. These accelerated styles are part of the USER-CUDA, GPU, USER-INTEL, KOKKOS, USER-OMP and OPT packages, respectively. They are only enabled if LAMMPS was built with those packages. See the :ref:`Making LAMMPS ` section for more info. You can specify the accelerated styles explicitly in your input script by including their suffix, or you can use the :ref:`-suffix command-line switch ` when you invoke LAMMPS, or you can use the :doc:`suffix ` command in your input script. See :doc:`Section_accelerate ` of the manual for more instructions on how to use the accelerated styles effectively. ---------- Restrictions """""""""""" This dihedral style can only be used if LAMMPS was built with the CLASS2 package. See the :ref:`Making LAMMPS ` section for more info on packages. Related commands """""""""""""""" :doc:`dihedral_coeff ` **Default:** none ---------- .. _dihedral-Sun: **(Sun)** Sun, J Phys Chem B 102, 7338-7364 (1998). .. _lws: http://lammps.sandia.gov .. _ld: Manual.html .. _lc: Section_commands.html#comm