1.. index:: improper_style cossq 2.. index:: improper_style cossq/omp 3 4improper_style cossq command 5============================ 6 7Accelerator Variants: *cossq/omp* 8 9Syntax 10"""""" 11 12.. code-block:: LAMMPS 13 14 improper_style cossq 15 16Examples 17"""""""" 18 19.. code-block:: LAMMPS 20 21 improper_style cossq 22 improper_coeff 1 4.0 0.0 23 24Description 25""""""""""" 26 27The *cossq* improper style uses the potential 28 29.. math:: 30 31 E = \frac{1}{2} K \cos^2{\left(\chi - \chi_0\right)} 32 33where :math:`\chi` is the improper angle, :math:`\chi_0` is its 34equilibrium value, and :math:`K` is a prefactor. 35 36If the 4 atoms in an improper quadruplet (listed in the data file read 37by the :doc:`read_data <read_data>` command) are ordered I,J,K,L then 38:math:`\chi` is the angle between the plane of I,J,K and the plane of J,K,L. 39Alternatively, you can think of atoms J,K,L as being in a plane, and 40atom I above the plane, and :math:`\chi` as a measure of how far 41out-of-plane I is with respect to the other 3 atoms. 42 43Note that defining 4 atoms to interact in this way, does not mean that 44bonds necessarily exist between I-J, J-K, or K-L, as they would in a 45linear dihedral. Normally, the bonds I-J, I-K, I-L would exist for an 46improper to be defined between the 4 atoms. 47 48The following coefficients must be defined for each improper type via 49the :doc:`improper_coeff <improper_coeff>` command as in the example 50above, or in the data file or restart files read by the 51:doc:`read_data <read_data>` or :doc:`read_restart <read_restart>` 52commands: 53 54* :math:`K` (energy) 55* :math:`\chi_0` (degrees) 56 57---------- 58 59.. include:: accel_styles.rst 60 61---------- 62 63Restrictions 64"""""""""""" 65 66This improper style can only be used if LAMMPS was built with the 67MOLECULE package. See the :doc:`Build package <Build_package>` doc 68page for more info. 69 70Related commands 71"""""""""""""""" 72 73:doc:`improper_coeff <improper_coeff>` 74 75Default 76""""""" 77 78none 79