.. index:: angle_style class2 angle_style class2 command ========================== angle_style class2/omp command ============================== Syntax """""" .. parsed-literal:: angle_style class2 Examples """""""" .. parsed-literal:: angle_style class2 angle_coeff * 75.0 angle_coeff 1 bb 10.5872 1.0119 1.5228 angle_coeff * ba 3.6551 24.895 1.0119 1.5228 Description """"""""""" The *class2* angle style uses the potential .. image:: Eqs/angle_class2.jpg :align: center where Ea is the angle term, Ebb is a bond-bond term, and Eba is a bond-angle term. Theta0 is the equilibrium angle and r1 and r2 are the equilibrium bond lengths. See :ref:`(Sun) ` for a description of the COMPASS class2 force field. Coefficients for the Ea, Ebb, and Eba formulas must be defined for each angle type via the :doc:`angle_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 4 coefficients for the Ea formula: * theta0 (degrees) * K2 (energy/radian^2) * K3 (energy/radian^3) * K4 (energy/radian^4) Theta0 is specified in degrees, but LAMMPS converts it to radians internally; hence the units of the various K are in per-radian. For the Ebb formula, each line in a :doc:`angle_coeff ` command in the input script lists 4 coefficients, the first of which is "bb" to indicate they are BondBond coefficients. In a data file, these coefficients should be listed under a "BondBond Coeffs" heading and you must leave out the "bb", i.e. only list 3 coefficients after the angle type. * bb * M (energy/distance^2) * r1 (distance) * r2 (distance) For the Eba formula, each line in a :doc:`angle_coeff ` command in the input script lists 5 coefficients, the first of which is "ba" to indicate they are BondAngle coefficients. In a data file, these coefficients should be listed under a "BondAngle Coeffs" heading and you must leave out the "ba", i.e. only list 4 coefficients after the angle type. * ba * N1 (energy/distance^2) * N2 (energy/distance^2) * r1 (distance) * r2 (distance) The theta0 value in the Eba formula is not specified, since it is the same value from the Ea formula. ---------- 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 angle 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:`angle_coeff ` **Default:** none ---------- .. _angle-Sun: **(Sun)** Sun, J Phys Chem B 102, 7338-7364 (1998). .. _lws: http://lammps.sandia.gov .. _ld: Manual.html .. _lc: Section_commands.html#comm