.. index:: improper_style class2 improper_style class2 command ============================= improper_style class2/omp command ================================= Syntax """""" .. parsed-literal:: improper_style class2 Examples """""""" .. parsed-literal:: improper_style class2 improper_coeff 1 100.0 0 improper_coeff * aa 0.0 0.0 0.0 115.06 130.01 115.06 Description """"""""""" The *class2* improper style uses the potential .. image:: Eqs/improper_class2.jpg :align: center where Ei is the improper term and Eaa is an angle-angle term. The 3 X terms in Ei are an average over 3 out-of-plane angles. The 4 atoms in an improper quadruplet (listed in the data file read by the :doc:`read_data ` command) are ordered I,J,K,L. X_IJKL refers to the angle between the plane of I,J,K and the plane of J,K,L, and the bond JK lies in both planes. Similarly for X_KJLI and X_LJIK. Note that atom J appears in the common bonds (JI, JK, JL) of all 3 X terms. Thus J (the 2nd atom in the quadruplet) is the atom of symmetry in the 3 X angles. The subscripts on the various theta's refer to different combinations of 3 atoms (I,J,K,L) used to form a particular angle. E.g. Theta_IJL is the angle formed by atoms I,J,L with J in the middle. Theta1, theta2, theta3 are the equilibrium positions of those angles. Again, atom J (the 2nd atom in the quadruplet) is the atom of symmetry in the theta angles, since it is always the center atom. Since atom J is the atom of symmetry, normally the bonds J-I, J-K, J-L would exist for an improper to be defined between the 4 atoms, but this is not required. See :ref:`(Sun) ` for a description of the COMPASS class2 force field. Coefficients for the Ei and Eaa formulas must be defined for each improper type via the :doc:`improper_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 2 coefficients for the Ei formula: * K (energy/radian^2) * X0 (degrees) X0 is specified in degrees, but LAMMPS converts it to radians internally; hence the units of K are in energy/radian^2. For the Eaa formula, each line in a :doc:`improper_coeff ` command in the input script lists 7 coefficients, the first of which is "aa" to indicate they are AngleAngle coefficients. In a data file, these coefficients should be listed under a "AngleAngle Coeffs" heading and you must leave out the "aa", i.e. only list 6 coefficients after the improper type. * aa * M1 (energy/distance) * M2 (energy/distance) * M3 (energy/distance) * theta1 (degrees) * theta2 (degrees) * theta3 (degrees) The theta values are specified in degrees, but LAMMPS converts them to radians internally; hence the units of M are in energy/radian^2. ---------- Styles with a *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 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 improper 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:`improper_coeff ` **Default:** none ---------- .. _improper-Sun: **(Sun)** Sun, J Phys Chem B 102, 7338-7364 (1998). .. _lws: http://lammps.sandia.gov .. _ld: Manual.html .. _lc: Section_commands.html#comm